Geology Box

This box is all about the geology of the San Francisco Bay Area and Earth history. Students will learn about the rock cycle and the types of rocks that form under different conditions. Using this knowledge, students will investigate the rock layers exposed alongside the Caldecott Tunnel (Highway 24). Their explorations will reveal the geologic history of the San Francisco Bay area as it transitioned from ocean, to riverbed, to flood plain, to volcano, and then back to ocean again. In addition, students will research and create a timeline of life on the planet investigating the various life forms throughout the history of our planet and putting our own miniscule existence as human beings into the context of the enormity of Earth history.

1. Crayon Rock Cycle

Summary
What’s the big deal about rocks? They don’t move, aren’t flashy, and seem pretty useless to the untrained eye. However, geologists are rock detectives, discovering clues to the ancient past. If you know how to read them, rocks can tell an observant scientist about what a place looked like millions and even billions of years ago. This activity introduces the 3 main types of rocks and the processes that form them. Wax crayons are eroded into sediment, compacted into sedimentary rock, partially melted and pressed into metamorphic rock, and finally melted and cooled into igneous rock. This understanding is the basis of the rock cycle. In the Going Further section, there is a recipe for making your own sandstone, siltstone and conglomerate using sediments and a sodium silicate solution.

Objectives
Can describe the 3 major types of rock (sedimentary, metamorphic, and igneous) and discuss the relationships between them
Can diagram the rock cycle
Given one of the three major types of rock, can describe the geologic processes that formed it

Vocabulary

1. Crayon Rock Cycle - Logistics

Time
45-50 minutes

Grouping
individual

Materials
Each student needs:

Copy of the Rock Cycle Diagram
1 wax crayon (Crayola brand crayons works well)
1 plastic knife
6 inch square of aluminum foil
Styrofoam or other cup to hold hot water
Source of hot water (I use a hot pot style electric water heater - see image)

32 oz Hot Pot Express by RivalA

For the whole class:

Samples of sedimentary, metamorphic, and igneous rock, sorted into boxes of the same rock type
3-6 large containers or water pitchers for water that has cooled down in the students’ cups

Setting

1. Crayon Rock Cycle - Background

Teacher Background
The rock cycle is perhaps the most basic, fundamental principle of geology. All rocks are related to each other and may be transformed from one kind to another. In its simplest form, the rock cycle describes the relationships between the 3 major types of rock:

Igneous Rocks - Formed from the cooling of molten rock (magma).
Sedimentary Rocks - Formed from layers of sediment as the pressure of overlying layers compacts the sediment into rock. Sometimes, a cementing agent, dissolved minerals such as silica or carbonates, helps bind the sediment particles together.
Metamorphic Rocks - Formed from other rocks that are exposed to intense heat and pressure and thus change their physical and/or chemical form.

Molten rock or magma solidifies either rapidly at the Earth’s surface or slowly under the Earth’s surface into igneous rock (this is the whole crayon we start with). As these rocks are exposed to erosion and weathering, they are broken down into sediment (a pile of crayon shavings). The grains of sediment may be transported long distances by water, wind or gravity, and eventually deposited in layers. As more and more sediment layers build up on top of each other, the sediments are compacted and sometimes cemented together into sedimentary rock (squishing the crayon shavings together) in a process called lithifaction. With heat and pressure (partial melting in hot water), the rock will undergo a physical and/or chemical change into metamorphic rock. If the rock is melted completely and cooled, you once again have igneous rock.

The rock cycle is attributed to James Hutton (1726-1797), the “father of geology” who meticulously explored and documented the landscape of the British Isles. Hutton proposed the principle of uniformitarianism, the idea that the processes that shape the world today also operated in the past. His idea brought about the revolutionary notion that given how long it takes for geologic processes to occur today, the Earth must be very very old for all the existing landforms to have been created, not merely the 6000 years allowed by tracing Biblical genealogy. One of his most famous quotes states that with respect to the Earth there is “no vestige of a beginning, and no prospect of an end”.

Portrait of James Hutton, 1726-1797, by Sir Henry Raeburn. From the collecctions of the National Galleries of Scotland.

With greater scientific sophistication and the plate tectonics revolution, many geologists now believe that the basic rock cycle described in this lesson is too simple. The basic rock cycle is cyclical, with no apparent direction or trend. Instead, if plate tectonics is taken into account, there may indeed be a trend towards greater and greater diversity of rock types over time. For more information, see the Tectonic Rock Cycle

Student Prerequisites
It helps the discussion of sedimentary rocks if students are familiar with soil separation and identifying different sediments (gravel, sand, silt, clay) by size. See Soil Analysis Lesson, Erosion Patterns Lesson and/or the Sediment Study Project.

1. Crayon Rock Cycle - Getting Ready

Getting Ready

Rip sheets of aluminum foil into 6 inch squares
Set out remaining materials – crayons, knives, cups, and hot water source
Copy Rock Cycle Diagram handout
Sort the rock samples into the 3 main categories of rocks if they aren’t already sorted

1. Crayon Rock Cycle - Lesson Plan

Lesson Plan

Pass around samples of sedimentary rock. Ask students to observe the rocks and describe some of the similarities between them. As students offer their ideas, write them on the board in one column. You should end up with a list like: First rock type: can see grains, grains can be of different sizes, has layers or streaks, grains come off if you rub it.
Collect the sedimentary rocks then pass around samples of metamorphic rocks. Ask students to observe the rocks and describe how these rocks are different from the sedimentary rocks. Again, write their ideas in a column on the board. You should end up with a list like: Second rock type: no grains, has crystals, many colors, very hard, swirly patterns.
Collect the metamorphic rocks then pass around samples of igneous rocks. Ask students to observe the rocks and describe how these rocks are different than the other two types of rocks. Again, write their ideas in a column on the board. You should end up with a list like: Third rock type: no grains, some have crystals, some have lots of holes, uniform texture and pattern throughout the rock, no layers or swirls.
Tell the students that they have been observing and categorizing the 3 major types of rocks: sedimentary, metamorphic, and igneous rocks. Explain that today, they will be using crayons to model the processes that create each of these 3 types of rock.
Pass out the handout, crayons, foil, and knife.
Tell students that they have been given a sample of a crayon rock. Looking at the 3 descriptions on the board, which one is this sample most similar to. It doesn’t have grains, layers or streaks. Thus it is an igneous crayon rock! On their handout, in the box at the top of the circle, have students write “igneous rock”.
The first step is to create sediment. Have students unwrap their crayons then create a pile of crayon shavings on their piece of aluminum foil by scraping it with the knife. They may trade crayons among themselves to acquire a mixture of colors. Give them around 5 minutes to build up a decent sized pile.
On the diagram, the arrow from “igneous rock” can be labeled “erosion”. The next box can be labeled “sediment”.
Now fold over the foil to wrap up the sediment pile. Press down on the pile as hard as you can. Gently unwrap it. The sedimentary crayon rock will be fragile but should hold together in a packed layer.
Discuss the similarities between the sedimentary crayon rock and the real sedimentary rocks the students observed earlier.
On the diagram, the arrow from “sediment” can be labeled “lithifaction – compacting and cementing sediments together”. The next box can be labeled “sedimentary rock”. Discuss this process as it occurs in the real world with layers being squeezed under other layers.
Now get a helper to pass out the cups and go around yourself to fill each cup with hot water. Have another helper place containers for cooled water near each table or cluster of desks.
Each student should create a little boat for their sedimentary crayon rock and float his or her boat on the hot water. Watch as the heat from the water melts the crayon. Remove the foil when the wax is soft to the touch and the colors have swirled together but not so much that the colors are indistinguishable. Let the metamorphic crayon rock cool.
Discuss the similarities between the metamorphic crayon rock and the real metamorphic rocks the students observed earlier.
On the diagram, the arrow from “sedimentary rock” can be labeled “metamorphism – heat and pressure transforms the rock”. The next box can be labeled “metamorphic rock”. Discuss this process as it occurs in the real world with rocks being subjected to intense heat and pressure beneath the surface of the Earth.
At this point, the temperature of the water the cups may have cooled. Ask students to dump their water into the containers. Go around and refill each cup with hot water.
Each student should put their metamorphic crayon rock back in the foil boat and float it on the hot water. This time, allow the wax to melt until a smooth pool of liquid wax forms and the colors blend together uniformly. Carefully remove the foil and let the igneous crayon rock cool.
Discuss the similarities between the igneous crayon rock and the real igneous rocks the students observed earlier.
On the diagram, the final arrow from “metamorphic rock” can be labeled “melting into magma then cooling”. Discuss this process as it occurs in the real world with rocks being melted deep within the Earth then extruded again as volcanoes or bubbles of magma that do not reach the surface.
Ask the students if they think this igneous rock could be turned into sedimentary rock? How? Could it be turned directly into metamorphic rock? How? Could a metamorphic rock be turned directly into sedimentary rock? How?
Add additional arrows across the middle of the rock cycle to illustrate that any type of rock can turn into any other type of rock.
If there is time, students can experiment with turning their igneous crayon rock into a new sedimentary, metamorphic, or igneous crayon rock.
Clean up! Students can keep their crayon rocks.

1. Crayon Rock Cycle - Assessments

Assessment

9th grade teacher Marcie Krech, has a list of great extension activities related to the rock cycle. They include a vocabulary cut & paste, a lab, a whole class puzzle, a game and a comic strip activity. In fact, Marcie has put her whole Earth Science curriculum online for others to learn from. Thank you!
Give students rocks to classify as sedimentary, igneous, or metamorphic.

Going Further

Make sedimentary rocks! Any sediment (powdered clay, silt, playground sand, or a sand and gravel mixture) can be turned into a sedimentary rock with the addition of a dilute sodium silicate solution. See the Sources section for where to purchase sodium silicate. The recipe:
- 15 ml dilute sodium silicate, dilute full strength sodium silicate with water in a 1 to 1 ratio (a 20 ml syringe is a great measuring tool and dispenser for this viscous solution)
- 6 tablespoons of sediment (playground sand works great although kids like to mix and match sediments for their own special rock type)
Mix the sediment and sodium silicate in a clear plastic 9 oz cup with a disposable stirrer like a popsicle stick. Be careful not to get sodium silicate on your hands or in your eyes. Smooth out the surface of the mixture with the stirrer. Set aside for 2 days. Once the mixture is completely dry, it can be popped out of the cup and examined up close. If you plan on doing the Layers Upon Layers lesson, consider adding layers of a different sedimentary rock on top of the first before removing the rock from the cups. You are, in effect, creating a permanent version of the depositional cups formed in the Layers Upon Layers lesson.
Try the History of Rock lesson where students research a rock and discover the story of its formation.
The National Parks Service has a great collection of teacher lesson plans related to rocks and the rock cycle called Geodetectives. There are individual activities for each of the 3 main rock types, a candy rock cycle activity, and a brilliant idea for comparing rocks to identify which rocks are best used for what purposes – building a house, tools, jewelry, etc.

1. Crayon Rock Cycle - Sources and Standards

Sources
The best write up for the crayon rock cycle activity is available from Eric Muller of the Exploratorium’s Teacher Institute. Go to The Crayon Rock Cycle. Eric has developed many other fantastic activities, particularly for Earth Science.

For additional information about the rock cycle, go to:

Rocksandminerals.com
The Department of Geology at James Madison University
Wikipedia

Sodium silicate solution (also called water glass) can be purchased from most science supply companies such as Flinn Scientific and Science Kit & Boreal Labs. A 500 ml bottle costs $5-6. Sometimes it can be found at marine supply stores in quart sized containers for sealing the outside of boats.

Standards
Grade 6
Plate Tectonics and Earth's Structure
Plate tectonics accounts for important features of Earth's surface and major geologic events. As a basis for understanding this concept:
a Students know evidence of plate tectonics is derived from the fit of the continents; the location of earthquakes, volcanoes, and midocean ridges; and the distribution of fossils, rock types, and ancient climatic zones.

Shaping Earth's Surface
Topography is reshaped by the weathering of rock and soil and by the transportation and deposition of sediment. As a basis for understanding this concept:
a Students know water running downhill is the dominant process in shaping the landscape, including California's landscape.
b Students know rivers and streams are dynamic systems that erode, transport sediment, change course, and flood their banks in natural and recurring patterns.

2. History of Rock

Summary
Every rock holds clues about how it formed. Geologists are like rock detectives who know how to read the clues about a rock’s origins and the stories it can tell. In this activity, students first become specialists in one type of rock. Then, they meet specialists in other rock types to compare their rocks and teach the others about their rock’s history. This lesson is an opportunity for students to consolidate information from the previous lesson on the rock cycle, and begin to think like geologists. Ideally, the rocks selected for investigation are collected from the site of an upcoming geology field trip – such as to the Caldecott Tunnel or Mount Diablo. In this way, students gain experience identifying individual rocks and learning about the way in which each of the different rock types form. Then, on the field trip, students can apply their controlled classroom knowledge to real world geological history.

Objectives
Can describe the 3 major types of rock (sedimentary, metamorphic, and igneous) and discuss the relationships between them
Can make careful observations of rocks, including conducting tests for hardness
Can use observations to identify an unknown rock as sedimentary, metamorphic, and igneous
Can describe the geologic processes that formed each of the 3 major types of rock

Vocabulary
Sedimentary rock
Mudstone
Sandstone
Conglomerate
Metamorphic rock
Igneous rock
Basalt
Granite

2. History of Rock - Logistics

Time
5 min introduction
15 min make observations and become experts
20-30 min rearrange into new groups, share expertise, and compare rocks

Grouping
Students will begin in teams organized by rock type. They will become specialists on that one type of rock. They will then rearrange into teams with one representative of each rock type and will compare their rocks and tell each other the histories of the rock they studied.

Materials

Several samples of rock from the field trip site you intend to visit. In my classes, to prepare for the Caldecott Tunnel field trip, I used mudstone, sandstone, conglomerate, granite and basalt. You need one rock per student, and an equal number of rocks of each type – for instance, if you have 25 students in your class and 5 different types of rock, you will need 5 samples of each type of rock for a total of 25 rocks.
Copy of the Rock History Data Sheet for each student.
Penny, one for each rock type
Butter knife or glass slide, one for each rock type
Optional: steel file, one for each rock type
Optional: hand lenses

Setting

2. History of Rock - Background

Teacher Background
In my classes, I used this lesson to prepare students for the Caldecott Tunnel field trip. Therefore, the rocks described in the teacher background section relate to those found in the cliffs of the Berkeley and Oakland hills. Additional sources for identifying common rocks that might be found in your backyard are provided in the Sources section. What follows is a brief introduction to sandstone, mudstone, conglomerate, basalt and granite.

**A special note on hardness testing**
Hardness testing is an easy test to determine the relative abrasion resistance of different minerals and rocks. Using an index material, like a fingernail with a hardness of 2.5, if your fingernail can scratch the surface of the rock you are testing, the rock has a hardness of less than 2.5. However, if the rock can scratch the surface of your fingernail, then the rock has a hardness of more than 2.5. By using a variety of common objects for comparison (fingernail – 2.5, penny – 3.5, butter knife or glass – 5.5, steel file – 6.5) you can easily approximate the hardness of your mystery rock. Unfortunately for this lesson, hardness tests are most useful for minerals that are composed of a pure substance of uniform density. In contrast, the hardness of a rock that is composed of a mixture of minerals will vary depending on the type of minerals in the rock and also how tightly bound the particles are to one another. For instance, a sandstone may be composed mainly of quartz grains with a hardness of 7 that can scratch steel, yet the rock itself might crumble in your hand. Thus, while hardness testing is a standard skill for geologists that want to know the mineral content of a rock, don’t rely on the measurements to identify the rock itself.

Sandstone
Sandstone is probably the most well known of the sedimentary rocks. It varies in color from red to brown, grey to white, sometimes with a tinge of green or yellow. It is usually composed of rounded sand particles that are medium grained, approximately the texture of beach sand. Sand is produced from the weathering of other rocks (like granite, sandstone and basalt). The sediment in a sandstone may have come from a sandbar along a river, an ocean beach, or desert sand dunes. As more and more sand layers accumulate on top on one another, the weight of the topmost layers compacts the sediment into rock. Often, minerals dissolved in water seeps down into the sandstone, cementing the rock together. The hardness varies greatly, between 2-7, depending on how tightly the sediment was compacted and cemented together.

Mudstone
Mudstone is a sedimentary rock similar to sandstone except that it is made of clay and silt-sized particles. The grains are generally indistinguishable from one another with the naked eye. Technically, mudstone is a mixture of clay and silt-sized particles. Shale is entirely clay-sized particles while siltstone is entirely silt-sized particles. It forms in areas such as lakes, deltas and flood plains where water slows to a near standstill and the smallest particles of trapped sediments are able to be deposited. The hardness is generally low, between 2-3.

Conglomerate
Conglomerate is a sedimentary rock similar to sandstone except that it contains chunks of rounded rocks and gravel. These are formed in fast-moving rivers where the water washes away all but the largest rocks. The hardness varies greatly, between 2-7, depending on how tightly the sediment was compacted and cemented together.

Basalt
Basalt is the most common type of rock on the Earth’s surface. Most of the ocean floor is composed of basalt. It is an igneous rock, formed from magma that cools at the Earth’s surface as it erupts from a volcano. It is generally dark in color, from black to dark grey although the rocks near Caldecott Tunnel are weathered to a dark red-brown. It has a hardness of 5-6 and is so fine grained that you need a microscope to be able to see the crystallization pattern. If it cools quickly, it forms a glassy, obsidian surface. Often, air pockets develop within the basalt as it cools, creating a distinctive holey texture like a sea sponge.

Granite
Granite is rapidly becoming the favorite surfacing material in kitchens. It comes in nearly every color of the rainbow, from pink to green to brown to black to white depending on the minerals and inclusions in the rock. The most distinctive feature of granite is crystals of varying color and size, randomly distributed throughout the rock. Granite is very hard, between 6-8 on the Moh’s hardness scale. It forms deep under the Earth’s crust as balloons of magma become trapped under the crust and slowly cools over thousands of years. Thus, granite often forms near subduction zones, where old crust is melted and rises up under the continental shelf. Most of the Sierra Nevadas is made of granite.

Student Prerequisites
A clear understanding of the rock cycle. See the Crayon Rock Cycle lesson.

2. History of Rock - Getting Ready

Getting Ready

Make copies of the Rock History Data Sheet.
Collect rock samples.
Collect rock observation tools: hardness testing materials and hand lenses.

2. History of Rock - Lesson Plan

Lesson Plan

Describe the goals of the day – to become an expert on a specific type of rock then share that expertise with other students in small groups.
Divide students into teams. A fun way to do this is to hand each student a rock when they walk through the door. Tell them not to show their rock to anyone. Once everyone has arrived, have them write down 5 observations about their rock on a sheet of paper. Silently, they should try to find the others with the same rock type based on the observations they wrote down. When everyone is sorted, they should reveal their rocks to see if they are in the right group.
Give each group a set of rocks of the same type and a Rock History Data Sheet. Carefully go over the observations the students need to make, particularly the procedure for hardness testing. Allow at least 15 minutes for students to make their observations and to discuss and describe their rock’s history in as much detail as possible. As they work, circulate among the groups, giving assistance where needed.
When all groups are finished, have students number off within the groups and rearrange them into new teams with one expert on each type of rock.
The first task is for each rock expert to introduce their rock to the other students. Each student should present their observations and the history of their rock.

The second task is to set out all the rocks and make comparisons. Instruct each group should create a summary table comparing the different rocks. If students struggle with making a table, you might want to help them get organized by creating an example table on the board at the front of the room. For instance:

	Basalt	Granite	Mudstone	Sandstone	Conglomerate
Type
Color
Texture
Grain Size
Crystal Size
Layering
Hardness
Environment

Have each group turn in their summary table at the end of the period. If you are planning a geology field trip to visit these rocks in the field, these tables become very useful to remind students of how to identify them.

2. History of Rock - Assessments

Assessment

The summary tables and data sheets may be collected and graded.
A quiz on different rocks and their formation may be appropriate. For example:

______    1. This type of rock is formed when eroded pieces of other rocks and minerals are compacted and cemented together.
______   2. This type of rock is formed when other rocks are partially melted under high heat and pressure.
______   3. This type of rock is formed when magma cools.
______   4. This type of rock is often found in layers.
______   5. This type of rock often has swirls, bands, veins, and crystals within it.
______   6. This type of rock comes from volcanoes.
______   7. Sandstone is an example of this type of rock.
______   8. Basalt is an example of this type of rock.
______   9. Granite is an example of this type of rock.
______   10. The size of the particles that make up this type of rock tells you how fast the water was moving when the particles were deposited.

Going Further

Now that students have some experience with making observations of rocks, give each student a mystery mineral to observe, identify, and research. They should complete a Rock History Data Sheet on it and use mineral identification guides to discover the identity and history of their mineral. To up the challenge, give students minerals or metals with a more complicated history like silver ore or a geode.
To learn more about sedimentary rocks, try the Layers upon Layers lesson or make your own sedimentary rocks, described the Going Further section of the Crayon Rock Cycle lesson.

2. History of Rock - Sources and Standards

Sources
Many rock identification guides are available on the Internet. My favorites include:

The Rock Identification Guide by Don Perry offers a nicely organized dichotomous key that has been developed over years of testing with kids (http://www.rockhounds.com/rockshop/rockkey/).
The Rock Identification Project at Brooke Weston City Technical College has good resources, both for identifying rocks and for an online rock identification quiz.
For a much more detailed, teacher quality guide to rock identification, use this excellent guide from the Ministry of Energy, Mines and Petroleum Resources in British Columbia.
For superb pictures of rocks of different types including cross-sections and close-ups, see the Earth Science Education Unit from Keele University in the United Kingdom.

The Oxford University Museum of Natural History, which has a great kid-friendly guide to testing the hardness of minerals.
The San Diego Natural History Museum also has wonderful resources for mineral testing for educators and kids. On their website you can also learn about testing for color, luster, streak, and specific gravity.

Investigation and Experimentation
Scientific progress is made by asking meaningful questions and conducting careful investigations. As a basis for understanding this concept and addressing the content in the other three strands, students should develop their own questions and perform investigations. Students will:
a Develop a hypothesis.
b Select and use appropriate tools and technology (including calculators, computers, balances, spring scales, microscopes, and binoculars) to perform tests, collect data, and display data.

3. Layers Upon Layers

Summary

Soil Analysis

Erosion Patterns

Sediment Study Project

Going Further activity from the Crayon Rock Cycle lesson

Objectives
Can describe the environments in which different sedimentary rocks are formed
Can identify and explain Steno’s 3 laws of stratigraphy
Can apply the laws of stratigraphy to describe the relative age of sediment layers

Vocabulary
Stratigraphy
Law of Original Horizontality
Law of Superposition
Law of Lateral Continuity
Depositional Environment
Optional: Principle of Uniformitarianism

3. Layers Upon Layers - Logistics

Time
45-50 minutes

Grouping
Individual, although clusters of 4-6 students need to be able to share materials

Materials

Clear, plastic, 16 oz or 20 oz party cups, at least 1 per student plus 20-30 additional cups for students to share.
At least 6 different, dry “sediments” of different grain sizes and colors, around one shoebox-full of each: playground sand, beach sand, groundcover rocks, diatomaceous earth, aquarium gravel, powdered clay, garden soil, school-yard soil, etc. Have students bring in sediments they find interesting. The activity transforms readily into an art project if you can find “pretty” sediments: colored aquarium gravels, colored sand, etc.
Spoons
5 gallon bucket or other large container for collecting waste sand
Water
Optional: Squeeze box (see Sources)
Optional: Cafeteria style trays
Optional: Photographs showing rock layers such as the Grand Canyon or other cliff faces

Squeeze Box with horizontal sediment layers

Squeeze box after squeezing showing folding and faulting of the layers

Setting

3. Layers Upon Layers - Background

Teacher Background
In this activity, students gently layer sediments on top of one another as they learn about the basic principles of stratigraphy as laid out by Nicolas Steno. The key to the activity is to allow time for each layer to settle completely before adding additional layers on top. Thus, I alternate between adding a layer and writing down each of Steno’s laws. Another key is to slowly sprinkle sediments evenly across the surface of the water. If you dump them too quickly, the lower layers will be disturbed, particularly when adding a gravel layer on top of a clay or silt layer.

Nicolas Steno (1638-1686) was one of the founders of the principles of geology. He got his start in medicine and anatomy. His foray into geology came about when some fishermen caught a large shark and Steno had the opportunity to dissect it. Upon examining the shark’s teeth, Steno noticed their resemblance to stony objects found embedded in certain rocks called glossopetrae. While the prevailing thought of the time was that the glossopetrae fell from the sky or grew in the rocks, Steno argued that the glossopetrae were the teeth of ancient sharks. These ancient teeth were buried in sediments that, over time, became stone. This led Steno to study fossils and other geological ideas and propose the three principles that form the foundation of stratigraphy: the law of original horizontality, the law of superposition, and the law of lateral continuity.

The law of superposition states that in an undisturbed series of rock layers, the youngest layers are on the top and the oldest layers are on the bottom. For example, my husband and I stack the mail on a table in the kitchen. Often, the pile builds up for a week or more before we sort through it. The mail from Monday is at the bottom of the pile while the mail from Friday ends up at the top, with the mail from the rest of the week in a chronological sequence in between. Similarly, as sedimentary layers build up on top of one another, as long as the stack remains undisturbed, the layers will form a chronological sequence with the oldest on the bottom. Viewed from the side in cross-section, you can read the layers as you would a timeline. Similarly, as students build more and more layers of sediment on the first, they will observe that the first layer they made is on the bottom, with subsequent layers building on top of the first.

Naturally, this sequencing of rock layers can be changed by geological forces, just as the sequencing of mail is changed when I sort through the pile. In a river valley, the running water will erode away the uppermost young layers. On cliff faces near the ocean, the action of the waves may undercut a cliff enough to cause a chunk to plunge into the water below, bringing younger layers down to where the older layers should be. As plate tectonics acts on the Earth’s surface, older layers may be tilted sideways or pushed upward and exposed. Students can experiment with tilting their cup on a pencil partway through the activity, tilting the lower layers and causing future layers to be laid down flat, but at an angle with the bottommost layers. If you perform the activity with the squeeze box, you can demonstrate and discuss the effects of tectonic forces that folds and faults the layers and disturbs the series.

The last of Steno’s laws, the law of lateral continuity, states that when a sediment layer is laid down, it will extend in all directions until it runs our of material or hits a wall. Thus, the sediment layers are virtually continuous sheets that extend until there is no more sediment (like if you put sprinkle a very small spoonful of sediment into the cup and it can’t cover the entire surface) or until it hits a barrier (like the edge of each layer where it hits the side of the cup).

For a discussion of depositional environment, see the Background section in the Erosion Patterns lesson. For a discussion of the principle of uniformitarianism, see the Background section in the Crayon Rock Cycle lesson.

Student Prerequisites
Students need to understand how sedimentary rocks form (see Crayon Rock Cycle lesson) and know how water velocity affects the deposition of sediments (see Erosion Patterns).

3. Layers Upon Layers - Getting Ready

Getting Ready

Create a set of sediments for teams of 4-6 students to share. Each set should contain a 16-20 oz cup full of each sediment sample with a spoon in each cup. For easier clean up and transportation, place each set of cups on a cafeteria tray.
Set out additional cups
Build a squeeze box. With a 2 by 4, some sheets of Plexiglas, a section of PVC pipe, and a few hours, you can build a great squeeze box to model how geologic forces deform sedimentary layers. See Sources.

3. Layers Upon Layers - Lesson Plan

Simulated rock layers created by Stephen J. Reynolds showing the sequence of events in the formation of a canyon.

Lesson Plan

Begin the day by reviewing how sedimentary rock forms – deposited sediments are compacted and cemented together.
Describe how today we will model how layers of sediments are deposited and will use logic to derive rules or laws that can be used to examine layers of rock in the real world. You may want to review the principle of uniformitarianism – that the processes that shape the world today also operated in the past – if you covered that previously. By making observations from our models, we can make some assumptions about how sediment is deposited and how rock layers formed in the real world many thousands and millions of years ago.
Distribute 1 clear plastic cup to each student. Tell them to fill their cups a little less than 1/2 full with water. Students should also get out a pencil and a piece of paper or their lab notebooks to take notes on.
Place sets of sediments on the desks or tables where groups of 4-6 students can access it.
Tell students that they will be gradually creating several layers of sediment in their cups. We have added water to the cups because most sediment is transported and deposited by water. There are 2 important keys to this activity. First, it takes time for each layer to form, so listen to directions and don’t rush. Second, sediment should be slowly sprinkled into the cup in a nice even layer, so don’t dump spoonfuls in all at once or the layers on the bottom will be ruined by the sediment coming in from the top.
Ask students to pick one of the sediments. Carefully, gently, and slowly sprinkle 2 spoonfuls of sediment over the surface of the water. Spend a moment observing the sediment as it slowly settles on the bottom of the cup. Have students take a peek at their neighbor’s cups and observe any similarities and differences in the way the different types of sediment settle.
Optional: If you are using the squeeze box, add a layer of your own, dry, to the squeeze box.
Have students share some of their observations. Generally, one of the first observations will be that gravel settles fastest while the powdered clay stays suspended, perhaps even floating in a layer on the surface. Allow this observation to lead into a review of what was learned about how sediments are deposited according to the size of the grains – small particles are picked up easily by running water and deposited only when water becomes still while large particles are difficult to transport and are deposited first. You may also want to remind students of the guesses they made when observing sedimentary rocks – that mudstone must have come from somewhere with a lot of mud like a delta, bay, while conglomerate must have come from somewhere with a lot of gravel, like a fast-flowing river.
Summarize these ideas on the board and have students copy it into their notes or lab notebooks: “Depositional environment – The size of the grains in a rock tells you about the environment those grains were deposited in. Small grains, like clay and silt, are picked up easily by running water and deposited only when water becomes still, like in a lake, bay, or delta. Large grains are difficult to transport and are left behind in rivers when the silt and clay gets washed away.”
Look at the cups again. Even the silt should have mostly settled into a flat layer by now. Discuss the process that turns sediments into rock. Have students imagine real world sediment layers, perhaps on the bottom of a lake, and what would have to happen to turn those sediments into rock. What kind of rock would it be? What would it look like?
Students should pick a new sediment and add a second layer of 2 spoonfuls on top of the first. Remind students to add the sediment slowly by sprinkling. Spend a moment observing the sediment settle and comparing each others’ cups.
Optional: If you are using the squeeze box, add a second layer.
Ask the students to describe the surface of each layer. Answers should resemble: “It’s flat.” “It’s even.” “Even though the gravel layer is more bumpy than the other surfaces, all the layers are flat.” Probe a little deeper and ask why the layers are flat. Answers might include: “Because of gravity.” “Because the sediment drifts down through the water and collects on the bottom.”
Summarize these ideas and formalize it as the law of original horizontality. Write it down on the board. You can choose to tell students about Nicolas Steno or not depending on your goals. Students should copy the summary statement into their notes or lab notebooks: “Law of Original Horizontality – When layers are deposited, they settle in flat, horizontal layers.”
Quickly observe the cups again. Students should then add a third layer to their cup. Spend a moment making observations and comparisons.
Optional: IF you are using a squeeze box, add a third layer.
Ask students about what happens at the sides of the cup. Are there walls or sides on a lake or in the ocean or in a delta? How far would the layer continue if there were no walls? Discuss the spread of sediments in the real world. If it seems appropriate, suggest a mini-experiment that students can try in their cups, such as adding just a pinch of sediment or sprinkling sediment just in one place as the sediment flowing from a river might be dumped into a lake just in one place.
Summarize these ideas as the law of lateral continuity and write it down on the board. Students should copy it into their notes or lab notebooks: “Law of Lateral Continuity - when a sediment layer is laid down, it will extend in all directions until it runs our of material or hits a wall.”
Quickly observe the cups again. Students should then add another layer to their cup. Spend a moment making observations and comparisons.
Optional: IF you are using a squeeze box, add another layer.
Ask the students about the order of the layers. Where is the first, the oldest, layer? Where is the most recent layer? Discuss the ordering of layers.
Summarize these ideas as the law of superposition and write it down on the board. Students should copy it into their notes or lab notebooks: “Law of Superposition - in an undisturbed series of rock layers, the youngest layers are on the top and the oldest layers are on the bottom.”
Discuss what “undisturbed” means and what you could do to the cups to mess up that order. Answers might include: “Stir it up.” “Turn it upside down.” “Tilt it sideways.” “Crush the cup.”
Ask the students what might happen in the real world to disturb rock layers that form. Answers might include: “Erosion.” “Bulldozers.” “Earthquakes.” Discuss how each of these disruptions might affect the rock layers.
Optional: If you have prepared a squeeze box, you can now use it to demonstrate how tectonic forces might disturb rock layers. Show the students the layers in your box. Then, squeeze the box to observe how the layers fold and fault, changing the sequencing of the layers.
Suggest a final experiment to the students. Place a pencil below the edge of their cups, being careful not to let the contents spill. Discuss what forces in the real world might tilt a series of rock layers in this way. Now add a final layer to the tilted cup. Observe how the layer is laid down flat relative to the table and the surface of the water, but how the new layer lies at an angle to the layers below. Review each of the 3 laws with the students and see how each rule was affected by the tilted cup.
Finally, instruct the students to draw a side-view picture of the cup with their sediment layers. Ask them to label each layer with a description of the layer and the depositional environment that would have laid down that kind of sediment. They could also write a paragraph below the picture describing the sequence of events that created their cup.
A few minutes before the end of class, clean up. The sediments can be collected in large waste containers and the cups themselves can be thrown away.

3. Layers Upon Layers - Assessments

Assessment

Collect the labeled drawings and paragraphs.
Provide your own drawing of a cup with layers and ask the students to describe the series of events that led to the formation of the cup, just as they did with their own cups.

Going Further

Spend a day looking at photographs of rock layers in landscapes such as the Grand Canyon, Bryce Canyon, Petra, or other places with amazing rock layers. Teach about the formation of these places or have students independently research them.
Go on a field trip to look at rock layers and study the rock layers up close, making hypotheses about the depositional environments that formed each layer and the sequence of events that must have taken place. See the Caldecott Tunnel field trip description for an example.

3. Layers Upon Layers - Sources and Standards

Sources
The inspiration for this activity is the squeeze box, cleverly designed by Eric Muller of the San Francisco Exploratorium. Look under Earth Science for the Squeeze Box activity.

For more information about Nicolas Steno and stratigraphy see:

The book, The Seashell on the Mountaintop, by Alan Cutler, is a wonderful, easy read that chronicles the life of Nicholas Steno. He vividly describes the life and discoveries of this anatomist turned geologist turned priest.
A great summary of Steno’s life and work can be found on the University of California Museum of Paleontology’s website.
Earth Science Australia offers supremely well organized lecture notes for their geology course based on the work of Professor Stephen Nelson of Tulane University. The information about sedimentary rocks goes into wonderful detail about how to read sedimentary layers for clues about the environment where the sediments were deposited.
Pamela Gore of the Georgia Perimeter College has also provided a fabulous overview of the basic principles of stratigraphy.
Stephen J. Reynolds has created a gorgeous collection of simulated landscape images showing the sequence of events in the formation of canyons, buttes and other landforms.

Standards

Grade 6

Investigation and Experimentation
Scientific progress is made by asking meaningful questions and conducting careful investigations. As a basis for understanding this concept and addressing the content in the other three strands, students should develop their own questions and perform investigations. Students will:
e    Recognize whether evidence is consistent with a proposed explanation.
f    Read a topographic map and a geologic map for evidence provided on the maps and construct and interpret a simple scale map.
g    Interpret events by sequence and time from natural phenomena (e.g., the relative ages of rocks and intrusions).

Grade 7
Earth and Life History (Earth Sciences)
Evidence from rocks allows us to understand the evolution of life on Earth. As a basis for understanding this concept:
a Students know Earth processes today are similar to those that occurred in the past and slow geologic processes have large cumulative effects over long periods of time.
c Students know that the rock cycle includes the formation of new sediment and rocks and that rocks are often found in layers, with the oldest generally on the bottom.

4. My Time

Summary
This simple lesson gets students accustomed to reading a Geologic Time Scale and understanding the organization of the information contained in it by creating a Personal Time Scale using events from their own lives. Students list major life events then arrange them by relative time. Then, based on whatever organizational scheme makes the most sense to them, they divide their lives into eons. Each eon is divided into eras and each era into periods. Students can then view events in their own life with events in the history of Earth. In addition, they learn the difference between relative time (whether one event came before another) and absolute time (how many years ago something happened).

Objectives
Can organize personal events into a format similar to the Geologic Time Scale
Can read information presented in the format of a Geologic Time Scale
Can explain the difference between relative and absolute time

Vocabulary
Eon
Era
Period
Geologic time scale
Relative time
Absolute time

4. My Time - Logistics

Time
45 minutes

Grouping
Individual

Materials
Copy of the Personal Time Scale handout for each student

Setting
Classroom

4. My Time - Background

Teacher Background
Geologists organize time, not on a calendar, but on a geologic time scale. This is the principal vocabulary shared by geologists and paleontologists so that when one scientist talks about such-and-such period or such-and-such epoch, others know what general time frame he or she is talking about. While it is not necessary for middle school students to memorize the names of the various eons, eras and periods, it is important for them to know how to read and find information on a geologic time scale.

The geologic time scale is made possible by Nicolas Steno (see detailed information about him in the Background section of the Layers Upon Layers lesson). With Steno’s law of superposition, geologists could identify the relative age of various rock layers, and therefore, the relative ages of the fossils contained in the rocks.

After Steno, a major advance in geology came from William Smith (1769-1839), a surveyor and amateur geologist. In the process of his work as a surveyor, he carefully observed rock layers all across England. He noticed that the fossils not only differed from one rock layer to the next, but that the same sequence of fossils appeared wherever he looked. His observation came to be known as the principle of faunal succession – since layers of sedimentary rock contain fossils in a specific sequence, and since the relative age of rock layers can be determined by superposition, rock layers may be correlated in time by the fossils they contain. In one series of rock layers, fossils A, B, C, D, and E could be found from bottom to top. Elsewhere in England, fossils D, E, F, G, and H were found in sequence. Thus, rocks containing fossil G and H are younger rocks containing fossil A, even though they aren’t found in the same place.

This use of fossils to identify the order of rock layers in the overall stratigraphic column allowed Smith to create a complete geologic map of England. Moreover, the principle of faunal succession allowed geologists worldwide to organize rocks and fossils into their relative temporal order. Based on these observations, major differences in the types of fossilized organisms found led scientists to organize the time scale into broad categories called eons, then subcategories called eras, and so on through finer and finer divisions of time. Only recently, since the 1950’s with the invention of the mass spectrometer and its application towards the radiometric dating of rocks, has it been possible to determine the actual ages of rocks and the fossils they contain.

Student Prerequisites

4. My Time - Getting Ready

Getting Ready
Make copies of the Personal Time Scale handout.

4. My Time - Lesson Plan

Lesson Plan

Begin the day with a discussion of time. How do you think about historical events? Do you categorize events by decade? Do you categorize events by major turning points in history like the American Revolution and the Civil War? How about events in your own life? Do you categorize things by what school you attended? Do you categorize things by where you lived? Do you categorize things relative to major family events like the birth of a sibling or a divorce?
Today we will be organizing events like geologists do and become familiar with the format of the time scale used to organize information about Earth history.
Pass out the handouts and explain the general directions described on the first page:
- Create a list of 20 major events in your lifetime
- Place a number beside each event according to which happened longest ago (1) and which happened most recently (20)
- Rewrite the list in reverse chronological order, with the most recent at the top and the most long ago at the bottom
- To the new list, add information about exactly how many years ago the event occurred
The list so far is what geologists refer to as a relative or sequential timeline. This is what students created from information gathered at the Caldecott Tunnel if you did that field trip or in their summary paragraphs from the Layers Upon Layers lesson. Discuss the difference between relative time, ordering events by which happened first, and absolute time, the number of years ago each event happened. A relative timeline can be observed from rock layers just by reading it from bottom to top. But is it possible to observe the actual, absolute number of years ago a rock layer formed just by looking at it? No. You can determine absolute time for events from your own life because you can remember each event, but nobody can remember the exact, absolute age of a rock unless it’s a crayon rock or a homemade sedimentary rock. Scientists use special tools to find the absolute, number of years ago a given rock layer was formed. More on this in later lessons.
After the discussion about relative and absolute time, students can categorize events into a hierarchical series of time periods. Students should think about a logical way to divide their life events into 2 categories such as “before I started school” and “after I started school” or perhaps “when I lived in New York” and “when I lived in California”. These will form the largest divisions of your personal time scale and will be called eons.
Students should draw a horizontal line across the eon, era and period columns, dividing their table according to the criteria they chose. They should name the categories with a 1 word label that ends in the suffix –ian or –ic. For instance, “Preschoolian” and “Schoolian” or “Newyorkian” and “Californian”. In the eon column, they should write down the names they chose.
Now students should divide each of the eons into 2 or 3 eras based on a different criteria. For instance, the “Schoolian Eon” can be divided into the “Elementarian Era” and the “Middleschoolian Era”. Students should divide their tables by drawing a line across the era and period columns according to the criteria they chose and should write in the name of the eras.
Finally, students should divide each era into 2 or 3 periods, if that is possible. If an era contains only a single event, then you don’t have to divide it. Students should divide their tables by drawing a line across the period column and should write in the name of the period.
If you have remaining time, students can color their tables or share them with one another in small groups.

4. My Time - Going Further

Going Further
This activity is designed as a prelude to diving into the geologic time scale. See the Geologic Time on the Web lesson and the Marking (Geologic) Time lesson.

4. My Time - Sources and Standards

Sources
This activity was inspired by the lesson Sequencing Time by Judith Scotchmoor. I adapted the format of the Personal Time Scale to more closely resemble the Geologic Time Scale most often used by geologists. In addition to writing great lessons, Judith Scotchmoor is the Director of Education at the University of California Museum of Paleontology. More importantly, she has created the definitive web resource for educators trying to teach geology and Earth history. Here you can find detailed information about each eon, era, period and epoch in Earth History. Furthermore, you can learn about how the geologic time scale was created and how it is organized. These web resources are used extensively in the next lesson in this Geology Box – Geologic Time on the Web.

To learn more about William Smith, read the excellent popular science book The Map that Changed the World: William Smith and the birth of modern geology by Simon Winchester.

Standards
Grade 6
Investigation and Experimentation
Scientific progress is made by asking meaningful questions and conducting careful investigations. As a basis for understanding this concept and addressing the content in the other three strands, students should develop their own questions and perform investigations. Students will:
g Interpret events by sequence and time from natural phenomena (e.g., the relative ages of rocks and intrusions).

Grade 7
Earth and Life History (Earth Sciences)
Evidence from rocks allows us to understand the evolution of life on Earth. As a basis for understanding this concept:
g Students know how to explain significant developments and extinctions of plant and animal life on the geologic time scale.

5. Geologic TIme on the Web

Summary
The University of California Museum of Paleontology (UCMP) created a fabulous introduction to the geologic time scale on the web called “Understanding Geologic Time”. Students are led through a series of interactive web pages covering a wide range of earth history concepts: relative vs. absolute time, the law of superposition, radiometric dating, the geologic timescale, and the origins and evolution of life on Earth. While the teacher section includes assessment materials including a “Scavenger Hunt” activity, I have included an alternative worksheet for students to follow as they navigate through the website and some extra credit questions in UCMP’s online “Geology Wing” for students that finish early. Links to activities that teach radiometric dating are included in the Going Further section.

Note: The simplicity of this lesson makes it appropriate for a substitute teacher to lead. On the other hand, the concepts covered are central to the curriculum and it is recommended that this lesson follows the Personal Timeline activity and precedes the Geologic Timeline activity.

Objectives
Can read information from a Geologic Time Scale
Can explain the difference between relative and absolute time and how each is inferred from geologic evidence
Develop a sense of the vastness of geologic time compared to everyday experience or even the existence of modern humans

Vocabulary
Relative time
Law of superposition
Absolute time
Radiometric dating
Eon
Era
Period
Geologic time
Geologic time scale

5. Geologic TIme on the Web - Logistics

Time
45 minutes

Grouping
Individual, although pairs of student sharing a computer also works well

Materials

Computers with Internet access, at least one per pair of students
Copies of the Geologic Time Web Activity handout

Setting

5. Geologic TIme on the Web - Background

Teacher Background
This lesson gradually leads students to a basic understanding of how the geologic timescale is organized and how it was created from evidence in rocks. See background information about Nicolas Steno (from the Layers Upon Layers lesson) and William Smith (from the My Time lesson) for preliminary background on arranging earth history by relative time. Below is a brief overview of determining the absolute age of rocks by radiometric dating. For a deeper understanding of the geologic time scale itself, see the Geologic Timelines lesson.

A great advance in the field of geology came in the form of the mass spectrometer, a device that measure the radioactive decay of elements. Simply put, each element in the periodic table contains the same number of protons but vary in the number of neutrons and thus can vary in their atomic weight. Atoms with the same number of protons but different numbers of neutrons are called isotopes. Over time, an unstable parent isotope will spontaneously eject parts of its nucleus and transform into a far more stable daughter isotope.

Geologists can use this to precisely determine the age of a rock layer, a method called radiometric dating. When a layer of igneous rock is laid down from a volcanic eruption, all the atoms begin as the parent isotope. Each parent isotope has a specific rate of decay that can be precisely timed. Some parent isotopes, like uranium-238 take an extremely long time to decay to the daughter isotope lead-206 (4.5 billion years for half of the uranium-238 in a given rock to decay to lead-206). Others have a very short decay rate or half-life (5,700 years for carbon-14 to decay to carbon-12). The ratio of parent to daughter element tells scientists precisely how old a given rock is.

Student Prerequisites
No experience is required although familiarity with determining the relative age of rock layers through the law of superposition (see Layers Upon Layers lesson) and with the general organization of the geologic time scale (see My Time lesson) is helpful.

5. Geologic TIme on the Web - Getting Ready

Getting Ready

Make copies of the Geologic Time Web Activity handout
Preview the teacher and the student sections of the “Understanding Geologic Time” website
Optional: bookmark links to “Understanding Geologic Time” (http://www.ucmp.berkeley.edu/education/explorations/tours/geotime/index.html) and the “Geology Wing” (http://www.ucmp.berkeley.edu/exhibit/geology.html) on the student computers. The urls are long and easily entered incorrectly by students.

5. Geologic TIme on the Web - Lesson Plan

Lesson Plan

Give students the student handout and allow them time to preview the questions they need to find answers to on the web.
Direct students to the “Understanding Geologic Time” website (http://www.ucmp.berkeley.edu/education/explorations/tours/geotime/gtpage1.html).
Give students 40-50 minutes to navigate their way through the website and answer the questions. Students who finish early can proceed to the back side of the handout and explore UCMP’s online “Geology Wing” (http://www.ucmp.berkeley.edu/exhibit/geology.html).
Collect the handouts when students are done.

5. Geologic TIme on the Web - Going Further

Going Further

Have students create timelines from the Geologic Time Scale that represent each of the eons, eras and periods of geologic time and the major biodiversity changes that occurred in each timeframe. See Geologic Timeline activity.
Teach students how radiometric dating occurs. The classic activity involves flipping 100 pennies or M&Ms in a shoebox and counting the “radioactive decay” of the parent isotope (pennium or eminemium) by counting and removing any that turn up heads. See this write up by Frank McKinney from UCMP or this version from the USGS Learning Web. For a variation where data is acquired from the class collectively, see this lesson plan from the Kentucky Geological Survey.

5. Geologic TIme on the Web - Sources and Standards

Sources
UCMP has a fabulous collection of web resources related to geologic time and paleontology called “Explorations Through Time”. Their description describes how these modules “explore the history of life on Earth, while focusing on the processes of science. Each module contains suggested lesson plans and an extensive teacher’s guide.” All are extremely well written and well worth a teacher’s time. This lesson is based on the “Understanding Geologic Time” lesson from this series.

For more information about radiometric dating, see:

The USGS provides excellent overview of radiometric dating.
How Stuff Works provides a very accessible overview of Carbon-14 dating in particular.

Standards

Grade 6

Grade 7
Earth and Life History (Earth Sciences)
Evidence from rocks allows us to understand the evolution of life on Earth. As a basis for understanding this concept:
b   Students know the history of life on Earth has been disrupted by major catastrophic events, such as major volcanic eruptions or the impact of an asteroid.
c   Students know the rock cycle includes the formation of new sediment and rocks. Rocks are often found in layers with the oldest generally on the bottom.
d   Students know evidence from geologic layers and radioactive dating indicate the Earth is approximately 4.6 billion years old, and that life has existed for more than 3 billion years.
e   Students know fossils provide evidence of how life and environmental conditions have changed.
g   Students know how to explain significant developments and extinctions of plant and animal life on the geologic time scale.

6. Geologic Timelines

Summary
For students, a few days can feel like a very long time. Thus, my students have a hard time conceptualizing the difference between 1 thousand, 1 million and 1 billion years. In this activity, students develop a sense of just how long the geologic time scale really is by creating a to-scale geologic timeline. This lesson begins with students guessing how long ago different events happened – when the Earth was formed, when life began, when dinosaurs roamed, and when humans first appeared. Then students redraw the periods and eras of the Phanerozoic Eon to scale using adding machine tape (1 million years = 1 millimeter). Then a teacher created scroll containing the other eons: Proterozoic, Archean and Hadean is unrolled to give students a visual sense of just how long Earth history really is. Finally, there are some analogies for students to contemplate, such as when different events would have occurred if Earth history were condensed into a calendar year or into a cross country trip.

Objectives
Can read information from a Geologic Time Scale
Recognize that many changes in biodiversity have occurred since life evolved on Earth
Can describe the major forms of life in each eon and in each era of the Phanerozoic Eon
Develop a sense of the vastness of geologic time

Vocabulary
Geologic time
Geologic time scale
Phanerozoic Eon
Proterozoic Eon
Archean Eon
Hadean Eon
Paleozoic Era
Mesozoic Era
Cenozoic Era

6. Geologic Timelines - Logistics

Time
10 minutes guess where events occurred and discussion
30 minutes create timescales
5 minutes add Pre-Cambrian eons to the timeline
5 minutes discuss analogies

Grouping
Individual

Materials

Copies of a geologic time scale (download the attachment on the bottom of the summary page, see the sources, or create your own)
Adding machine paper, at least 60 cm per student and an additional 5 meters for the class
Meter sticks or rulers, enough for 1 per student
Optional: Colored pencils
Optional: Calendar or map of the United States

Setting

6. Geologic Timelines - Background

Teacher Background
The major goal in this activity is for students to gain a sense of scale and a general feel for the vastness of geologic time. An understanding of the major biodiversity changes in the various eons and eras is secondary. The timelines students create use a 1 million years to 1 millimeter scale, resulting in a Phanerozoic eon that is 54 cm long and a geologic time scale that is 4.6 meters long. Students create only the more interesting Phanerozoic timelines while the full timeline is unrolled for dramatic effect near the end of the period.

The geologic time scale is a tool used by geologists to break up the history of Earth (all 4.6 billion years of it) into chunks that are more manageable. These divisions are determined by the major changes in biodiversity (and therefore the appearances of some fossils and the disappearance of others) that occurred throughout time. As new information is discovered, the geologic time scale is refined to refelect these new discoveries. The dates given in the handout are derived from a 2004 revision of the time scale endorsed by the International Commission on Stratigraphy. Several changes such as the phasing out of the Tertiary/Quaternary periods in favor of a Paleogene/Neogene division is included here.

The largest divisions are eons that define the most major developments in Earth’s history. The most ancient eon, the Hadean (from 4.6 – 3.8 billion years ago), finds the Earth as it coalesces and cools into a more stable planet. The first life appears in the form of ancient bacteria during the second eon, the Archean (from 3.8 – 2.5 billion years ago). Gradually, more complex eukaryotic life including algae and the first multicelluar organisms evolve during the third eon, the Proterozoic (from 2.5 – 0.54 billion years ago). These early photosynthetic organisms produced oxygen that accumulated in the Earth’s atmosphere. Finally, there is the Phanerozoic eon (from 542 million years ago to the present) encompassing the evolution of most complex life on Earth.

Eons are divided into eras that are in the range of hundreds of millions of years long. The major eras of the Pharnerozoic include the Paleozoic (from 542 – 251 million years ago), the Mesozoic (from 251 – 65 million years ago) and the Cenozoic (from 65 million years ago to the present). These can broadly be described as the “Age of Fish and Amphibians”, the “Age of the Dinosaurs”, and the “Age of Mammals”. Each era ended with a major extinction event. Following eras, the divisions of time are called: periods, epochs, and ages.

Student Prerequisites
Familiarity with the idea of relative and absolute time. Familiarity with the organization of the geologic time scale into eons, eras and periods is helpful.

6. Geologic Timelines - Getting Ready

Getting Ready

Make photocopies of the Geologic Time Scale.
Cut adding tape into 54 cm long strips, enough for one per student with a few extras for mess-ups.
Cut one strip of adding tape 4.6 meters long to show all 4 eons. On this strip, measure off the first 54 cm to represent the Phanerozoic eon, the next 2 meters to represent the Paleozoic eon, the next 1.3 meters to represent the Archean eon, and the last 80 cm represents the Hadean eon. Label each section accordingly. Roll the strip up again so that the most recent events are on the outside of the roll (start rolling from the Hadean eon end) and secure with a rubber band or paper clip.
On the board, draw a line across its entire length. Label the left end “The Earth and solar system form”. Label the right end “Today”. Below this write “Draw an arrow on the timeline where you think dinosaurs roamed the Earth. Draw a dot on the timeline where you think humans first appeared.”
Measure the line across the board and approximate where the Mesozoic era would be (65-250 mya = dinosaurs) and where the Neogene period began (23 mya = first hominids). Don’t label these places, just remember where they are approximately for later in the class.

6. Geologic Timelines - Lesson Plan

Lesson Plan

As students trickle into class, direct them to the front of the room and have them add an arrow or dot to the timeline on the board. (If this format is too chaotic for your classroom situation, add labels and tick marks every 200 million years or so and have students write down their numerical guesses on a sheet of paper in their seats.)
When all students have made a guess, briefly discuss their hypotheses. In particular, ask them about their reasoning behind their guesses.
Distribute the geologic time scale handouts. Give students a moment to see if they can determine how many years ago the Earth and solar system formed (4,570 million or 4.57 billion years ago). Allow the student that first discovers this information to explain how s/he figured out the answer. Point out how the geologic time scale has the most recent events on the top and the most ancient events on the bottom, just like rock layers.
Ask students to find out when dinosaurs roamed the Earth. This time, ask them to tell you not only how many million years ago but also during what eon, era, and periods dinosaurs lived. Again, allow the student who discover this information to share how s/he read the answer. Point out how the eon, era and period can be determined by the first 3 columns in the table.
Ask students to find out when the first humans appeared. Is this a long time ago compared to the entire history of Earth or a short time?
Give students a brief overview of the 4 major eons and the types of life that were present in each. Refer to the geologic time scale frequently to reinforce how to read information from the table.
Ask students which of these eons was the longest? Which was the shortest? How do you know? Point out that the timescale is not broken into even chunks of time. That some eons are longer than others, just as some eras are longer than others and some periods are longer than others. Thus, while the geologic time scale is good for finding information, it’s not an accurate way to visually see how long one chunk is compared to another.
Tell students that they will now create a timeline representing the most recent eon, the Phanerozoic. On the board write “1 millimeter = 1 million years; 1 centimeter = 10 million years”. Show students a strip of adding machine paper and hold a meter stick up next to it. Model for them how to keep the meter stick in the same place, with one end of the paper aligned with the 0 mark, and how to mark off boundaries between the eras and periods and label each mark with the number of millions of years ago that mark represents.
Give students their own adding machine tape and a meter stick. Remind them with your own set up how to mark off the boundaries between the periods using the meter stick and their time scales. Once they have the general idea, wander around the classroom helping individuals that are having difficulty.
Once the time boundaries are marked off, have students identify each period and write in the name of the period and one of the major biological events that happened in that period.
If you have time, have students color their time scales. I had my students color each of the eras a different color to visually link the periods in the same era together. Alternatively, you could color each period a different color.
When students are done or 10 minutes before the end of class, have a student that is finished hold up their timeline. Tell students that you created a timeline that includes all of Earth history, from when the Earth and solar system formed until today. Match the “today” end of your rolled up timeline with the “today” end of your student’s timeline. Unroll yours behind or below your student’s. When you reach the end of the Paleozoic, have a student come up to hold that section and briefly review the major events in that eon. Continue unrolling and stop again at the end of the Archaen eon to have a student hold that section and to review the major events. Finish in the same fashion with the Hadean eon.
With the remaining time, give students one or two analogies as “food for thought” to depart class with.

Geologic time as a calendar year:

Imagine that the geologic time scale is contained in 1 calendar year (each second is around 146 years). January 1 is 4.6 billion years ago.
The oldest known rocks are formed in early March
The first forms of life (bacteria and algae) are preserved as fossils in late March
The first multi-celled creatures (seaweed) appear on September 3
Phanerozoic Eon (most recent eon) begins on November 11
Reptiles appear on December 5
The first mammals appear December 14
Dinosaurs go extinct December 26
The first hominids (human-like ancestors) appear at 5 PM on December 31 (7 hours before midnight)
The first modern humans (Homo sapiens) appear at 11:48 PM on December 31 (12 minutes to midnight)
The last glacier receded at 11:58:45 p.m. on December 31 (1 minute and 15 seconds before midnight)
Written history begins at 11:59:30 on December 31 (30 seconds before midnight)
Columbus lands in the Americas 3 seconds before midnight
You were born 1/10th of a second before midnight

Geologic time as the distance from Los Angeles to New York City:

The distance from LA to NYC is approximately 4500 kilometers (km). Therefore, each kilometer represents one million years of Earth history. Look at a map of the United States. Start the geologic time journey in LA.
Precambrian would last until Pittsburgh
Paleozoic would be entirely in Pennsylvania
Mesozoic would get us to New Jersey, only 66 km from NYC.
The most recent Ice Age ended about 10,000 years ago. 10,000 years = 1/100 of a million years = 10 meters.
The past 2000 years of history would be represented by a sidewalk (2 meters)
A human lifespan would be half of the width of a curb (100 millimeters)

6. Geologic Timelines - Assessment

Assessment

This is a good time for a short quiz on the geologic time scale. Have students use their geologic time scales to find information. For example:
- The __________________________ is an outline of the major events in the earth's history. The largest grouping of time is a __________________. The next largest grouping of time is a __________________.
- Describe the forms of life that were around 190 million years ago.
- The first mammals appeared during the _________________ period in the __________________ era and ___________________eon.
Watch the movie “Ice Age” and critique the scientific inaccuracies in it using your geologic time scale.

Going Further

The Kentucky Geological Survey provides a fantastic list of ideas for how to modify this activity to create timeline showing the geologic time scale down a hallway, using calendars, across a school gym, using toilet paper, etc.
Study fossils. Learn about how fossils form (see Fossil Adventure lesson). Go on a archaeological dig. Go to a museum with fossils. Study the Mesozoic era and the rise and fall of dinosaurs (kids love dinosaurs).

6. Geologic Timelines - Sources and Standards

Sources
The geologic time scale used in this lesson was based on information from the International Commission on Stratigraphy and on Wikipedia.

The lesson itself was inspired by several other similar lessons including one by Judy Scotchmoor called “What Came First?” and a series of lessons by the Kentucky Geological Survey called It’s About Time.

If you don’t like the style of the Geologic Time Scale provided here, try these:

From the UC Museum of Paleontology. Definitely check out their geologic time machine where you can explore each period, era and eon in greater detail.
From the Geological Society of America. This version has the greatest level of detail I have seen.
From the British Geological Society.
From the Association of Professional Geoscientists of Ontario.
From geology.com.

The USGS provides a great, short overview of geologic time.
So does the Kentucky Geological Survey.

Standards

7. Choose Your Own Fossil Adventure

Summary
Fossils are extremely rare but also extremely exciting and rich with information about past life on Earth. In this lesson, students learn about the major types of fossils and how they form. They complete the lesson by illustrating and creating a “Choose Your Own Adventure” type story in which a Tyrannosaurus rex dies with 7 different possible endings, only one of which results in the discovery of its fossilized skeleton.

Objectives

Vocabulary
Fossil
Body fossils
Permineralization
Trace fossils
Mold fossils
Cast fossils

7. Fossil Adventure - Logistics

Time
20 minute class discussion on the types of fossils and how they form
30 minutes create the Choose Your Own Fossil Adventure book

Grouping
Individual

Materials

Pictures of different types of fossils (see sources for some recommendations of great websites if you don’t have access to books on fossils)
Copy of Choose Your Own Fossil Adventure pages
Scissors
Stapler
Optional: 8.5 X 11 paper
Optional: colored pencils or markers
Optional: a chunk of modeling clay or Playdoh

Setting

7. Fossil Adventure - Background

Teacher Background
No exploration of the geologic time scale is complete without thinking about fossils. Fortunately, kids love fossils. However, there are many common misconceptions – that fossils are fairly common, that every species that once lived must have been preserved in some way, that fossilized skeletons are often found intact. What students rarely understand is that fossils are extraordinarily rare. In fact, the vast majority of species that once lived on the planet vanished without a trace. Each and every fossil is precious because there are so few of them and because each fossil can provide so much information about past life on this planet.

Fossils are the preserved remains of former life or traces of them such as molds, casts, and footprints. The main categories of fossils include:

Body fossils – mineralized or preserved remains of body parts such as teeth, shells, bones or claws. The most common way body fossils form is by an organism being covered in sediment soon after death. The sediment provides a shield from damage by scavengers, weathering, and decay. The amount of time that passes before the organism is covered determines how much is eventually fossilized – if covered quickly by a sandstorm or landslide, an entire skeleton and even scales or hair may remain, whereas if covered slowly, only the most easily preserved hard tissue such as teeth may remain. As the layers of sediment build over thousands of years, the sediment layers become rock through compaction and cementation. At the same time, the remains of the organism decays and is slowly replaced with minerals that seep through the sedimentary rock, such as calcite, silica, and iron. This process by which body parts are replaced with rock is called permineralization. Different tissues are permineralized at different rates so even the internal details of bones and teeth may be preserved. In addition to permineralization, an animal or plant may become preserved in tar (the La Brea Tar Pits), in ice (several wooly mammoths have been discovered encased in Siberian ice), or in amber (insects are commonly preserved in amber).
Trace fossils – fossilized evidence of the behavior of past life such as footprints, nests, burrows, eggs, and droppings. Trace fossils are extremely precious because they provide information about the lifestyle and behavior of past life. Do they take care of their young? Do they live singly or in groups? How do they walk? Where do they live?
Mold fossils – a negative imprint of an organism preserved in stone. While the organism itself may decay without being preserved, the imprint remains in the sedimentary layers that eventually become sedimentary rock.
Cast fossils – a positive imprint of an organism preserved in stone. If a mold fossil is filled in with additional sediment, this second layer becomes a cast fossil.

Student Prerequisites
A good understanding of how sedimentary rocks form and of basic stratigraphy principles. Knowledge of the geologic time scale is helpful but not required.

7. Fossil Adventure - Getting Ready

Getting Ready

Find good fossil pictures in each of the 4 categories to show students (body fossil, trace fossil, mold/cast fossil)
Make copies of the Choose Your Own Fossil Adventure handout
Set out scissors, staplers, and colored pencils for students to share

7. Fossil Adventure - Lesson Plan

Lesson Plan

Have students write down on a piece of paper: what they know about fossils and what questions they have about fossils.
Spend 5 minutes allowing students to share what they know and the questions they have. You may want to write up some of their questions and knowledge on the board.
Summarize their responses into a general definition of “fossil” – the preserved remains of past life on earth or traces of their existence. Students may write this definition in their notes.
Next, tell students about the different types of fossils that might form: body, trace, mold, and cast fossils. As you describe each type, show students pictures of fossils and describe how each are formed. This is also an opportunity to review how sedimentary rocks form and the similarities between sedimentary rock formation and permineralization. You can model the formation of cast and mold fossils using clay or Playdough (make an imprint of your hand in clay or Playdoh and discuss how part of a plant or animal might create an imprint in mud or sediment).
Discuss what different kinds of information one might learn from body fossils such as a bone, trace fossils such as footprints or a nest, and mold/cast fossils such as plants. Throughout this discussion answer relevant questions from the students’ list.
Close this introductory portion by reviewing the process of permineralization and point out all the ways this process could be set off course – decomposed by bacteria, destroyed by scavengers, weathered to dust, crushed by too many layers of sediment, uncovered before fossilization, destroyed by earth forces, never uncovered by erosion, uncovered by erosion but washed away or eroded before being discovered, etc.
Finally, tell students that they will now put together a “choose your own adventure story” about fossil formation. A T rex has died and many things can happen to the carcass, only one of which leads to becoming a fossil. To make a very simple book, students should cut out each page of the story, assemble it by the page numbers at the bottom of each page, and then staple the pages together. If you want your students to illustrate the book, they can draw a picture on the back of the page before. Alternatively, take 3 sheets of regular 8.5 X 11 paper and fold them in half “hamburger-style”. The text for each page can be cut from the templates and pasted on the pages of your booklet. The remaining portion of each page can be used for illustration. For an even greater challenge, have students add their own “extra credit” pages with additional scenarios for their T rex skeleton. Students can have the rest of the class period to create their books.

7. Fossil Adventure - Assessment

Assessment

As homework, I had my students share their book with someone else that didn’t take my class: a parent, sibling, or friend. They had to read the story to this person until he or she discovered the path to making a fossil and discovery by a scientist. My students also had to answer any questions their “someone else” had about fossils.
Have students create a flow chart describing the process of permineralization.
Have students put describing the steps in fossil formation in the correct order:____   minerals in the ground water crystallize within the tiny crevices left behind as the muscle and bones decompose, slowly replacing the bones, teeth and claws with rock, turning the T rex into a fossil
____   a T rex dies near the edge of a river
____   T rex’s body gets covered in sediment and is protected from scavengers and from being destroyed by the weather
____   as millions of years pass, the layers of sedimentary rock that once surrounded the now fossilized T rex erode away
____   minerals in the ground water cement the sediment together to form sedimentary rock
____   a paleontologist discovers the fossils!
Have students explain in a paragraph why most of the past life on Earth vanished without a trace.

Going Further

Make your own fossils and have your students excavate them! Carol Mankiewicz and Carl V. Mendelson from Beloit College describe how to make trace fossils with plaster of paris and the footprints of a small classroom pet. Paul Belmas of Bannach Elementary describes how to make body fossils from chicken bones, sharks teeth, or other animal remains with plaster of paris and sand. Roger Evans creates a field trip experience with buried animal bones in an outdoor site.
Study a specific fossil (or set of fossils) in detail, drawing connections to the geologic time scale and stratigraphy. One fantastic lesson of many is the in depth study of the Laetoli footprints with this lesson by Steve Randak. These footprints offer indisputable evidence that by 3.6 million years ago, our human ancestors were walking on 2 legs. Students can study these footprints to investigate the height, stride length and walking speed of our ancient ancestors.

7. Fossil Adventure - Sources and Standards

Sources
This lesson was adapted from the “Fossil Finding” lesson by the Museum of the Rockies by including multiple possible endings besides the formation and discovery of a fossil. This and other excellent lessons may be downloaded from their website.

Another great explanation of how fossils form, with good pictures, can be found on the Discovering Fossils website.

Other great K-12 paleontology lessons may be found at:

Paleontological Experiences for Science Teachers by the University of Wisconsin
Learning from the Fossil Record by the UC Museum of Paleontology
Earth Science Classroom Activities from the Kentucky Geological Survey

For pictures of fossils, see:

The UC Museum of Paleontology’s online collections
The Smithsonian Institute’s online resources on Evolution and Paleontology
The Royal Tyrell Museum has great information about its exhibits

Standards
Grade 7
Earth and Life History (Earth Sciences)
Evidence from rocks allows us to understand the evolution of life on Earth. As a basis for understanding this concept:
a.   Students know Earth processes today are similar to those that occurred in the past and slow geologic processes have large cumulative effects over long periods of time.
e.   Students know fossils provide evidence of how life and environmental conditions have changed.
g.   Students know how to explain significant developments and extinctions of plant and animal life on the geologic time scale.

8. Dinosaur Extinction Theories

Summary Cartoon by Chris Madden

What caused the extinction of the dinosaurs? Was it a massive meteor? Was it the result of tremendous volcanic activity that covered the globe in volcanic ash? Was it the effects of gradual climate change? Was it the result of plate tectonics? Students are given a set of evidence cards that state scientific discoveries about rocks from 65 million years ago and prediction cards that discuss the predicted effects of different events such as a meteor impact, a rise in carbon dioxide levels, and plate tectonics. Teams of students are charged with assembling this information into an overarching theory that best explains the evidence at hand. At the end of the period or the following period, teams present their theories to the whole group and enter into a debate about the cause or causes of the great dinosaur extinction.

Objectives
Can sort through evidence and come up with a scientific theory that best fits the data.
Can recognize whether evidence is consistent with a scientific theory.
Can use geologic evidence to propose theories about past life on earth.

Vocabulary
Theory
Extinction
Mass extinction
K-T boundary
Iridium

8. Extinction Theories - Logistics

Time
5 minute introduction
40-50 minutes to come up with theories
45-55 minutes to present theories and discuss conflicting theories

Grouping
Groups of 3 students

Materials

1 set of evidence cards per team
1 envelope per team
1 “Dinosaur Extinction” worksheet per team

Setting

8. Extinction Theories - Background

Teacher Background
There have been many mass extinctions throughout the history of the Earth. A mass extinction may be defined as an episode in geologic history where over half of the species in existence become extinct in a relatively short amount of time (just a few million years). The worst mass extinction came at the end of the Paleozoic Era 245 million years ago when nearly 95% of plant and animal life in the seas disappeared. Another mass extinction may be happening today. Evidence from the fossil record shows that, on average, only 10-100 species become extinct per year. Some estimates show that current rates of extinction are as high as 27,000 species per year.

Probably the most famous mass extinction happened 65 million years ago when the dinosaurs disappeared. This is generally called the K-T extinction since it occurred at the boundary between the Cretaceous (K) and Tertiary (T) periods. Whatever triggered the extinction of the dinosaurs also caused the death of nearly 60-70% of all the other species on Earth. Interestingly, not all groups of organisms were affected equally. Ocean species were hit harder than land-based species, with 90% of them becoming extinct. Birds were the only survivors of the dinosaur lineage. Interestingly, mammals, lizards, snakes, and other smaller terrestrial creatures were hardly affected. For some reason, ferns actually expanded and thrived during this time.

So what caused the dinosaur extinction? The clues can be found in the rocks that date from 65 million years ago. Some pieces of evidence are agreed upon by nearly all scientists:

Around the time of the K-T extinctions, there was global climate change. What was once a warm, mild climate changed to one that was more varied (sometimes very hot, sometimes very cold).
In India, there was extensive volcanic activity, known as the Deccan Traps. Rocks that date from 65-68 million years ago in southern India are almost entirely igneous (volcanic). Almost 200,000 square miles was covered in lava over a period of 3 million years (an area equivalent to the entire mid-western United States). In some places, the lava beds are a mile deep.
A scientist called Alan Hildebrand found evidence of what is most likely an enormous asteroid impact site in the Yucatan region of Mexico. He called the 110 mile wide crater Chicxulub. The crater has been dated as 65.3 million years old (300,000 years before the mass extinctions). The size of the crater is comparable to that which would have been caused by an asteroid 6 miles wide.
Rocks that date from 65 million years ago contain high amounts of soot
Rocks that date from 65 million years ago contain unusual amounts of the rare element iridium. The levels of iridium contained in the rocks from this time period are roughly 30 times the normal levels. The most likely sources of high levels of iridium are:
- from outer space in the form of cosmic dust from a nearby exploding supernova
- from outer space carried to Earth by an asteroid or meteor
- from eruptions of massive volcanoes.
Major changes in the organization of the continents were occurring around 65 million years ago due to plate tectonics. There is evidence that the oceans were receding. For example, a shallow sea once covered what is now the mid-western United States. This sea drained away over several million years around the time of the dinosaur extinctions as the Colorado Plateau rose.

Gradualists – These scientists believe that the fossil record indicates a gradual decline over 5-10 million years. This time frame is more consistent with long term events such as plate tectonic forces and massive volcanic activity. These scientists believe that plate tectonic forces caused extensive volcanic activity in India and perhaps elsewhere that resulted in dense clouds of soot being released into the air. The soot darkened the skies resulting in global climate change and the reduced survival of plants, algae and plankton. In addition, the volcanoes likely released large quantities of carbon dioxide, further aggravating the climate through global warming and acid rain.

Catastrophists – These scientists believe that the fossil record indicates a sudden decline that is more consistent with a catastrophic event such as a massive asteroid impact. This theory was first proposed in 1980 by Walter Alvarez and is often referred to as the Alvarez Theory. He based his claims on the high iridium levels in rocks of that time period – suggesting that the isotopic profile of the iridium is more consistent with an extraterrestrial origin (a meteor or comet impact) than a volcanic origin. This is consistent with the presence of shocked quartz (metamorphically transformed quartz resulting from intense shock waves) in the rocks of that age. The resulting blast would have destroyed everything within 250-300 miles, including the object. Trillions of tons of debris (like dust, smoke, and steam) would have been thrown into the atmosphere when the object vaporized, darkening the sky around the globe in just a few weeks. Earthquakes, tsunamis, and wildfires would almost certainly have been triggered. The darkness may have only persisted for a few years but the effects on plant life would have been devastating.

The biggest problem with the catastrophic theory is that no conclusive crater has been identified. The most promising is evidence of an ancient crater called Chicxulub that was discovered in the Yucatan peninsula of Mexico. It is widely believed that Chicxulub is indeed the result of a massive asteroid nearly 6 miles across. Unfortunately, the crater itself is dated to 300,000 years before the K-T extinctions themselves. Could there have been another meteor impact or even a series of impacts? An even larger crater, the Shiva crater, was reported by Sankar Chatterjee under the Arabian Sea, off the coast of India. It is called the Shiva cater and dates from 65.0 million years ago. The Shiva crater is about 370 miles across and 7.5 miles deep. However, what created the crater is unknown. If it were made by an asteroid or meteoroid, the object must have been at least 25 miles wide. Other geologists claim the Shiva crater is the result of a sinkhole in the Earth’s surface, not an asteroid.

This ongoing debate offers an exciting opportunity for students to sort through the clues and propose a theory to explain the extinction of the dinosaurs. The key to this activity is for students to begin by organizing the evidence into sets of related information and then use the evidence to support a logical theory. Since there is no right answer students have an opportunity to engage in a true scientific debate over the same set of data that paleontologists, geologists, and astronomers argue over. Furthermore, there are endless directions in which the debate may travel, opening endless opportunities for further exploration.

Student Prerequisites
Students should have an understanding of how fossils form and have experience with the geologic time scale. It is helpful to have a good foundation in the rock cycle and stratigraphy so as to better understand how the evidence provided may have been gathered.

8. Extinction Theories - Getting Ready

Getting Ready

Make a copy of the “Dinosaur Extinction” handout for each team of students.
Copy and cut out a set of extinction cards for each team of students. Putting the cards on cardstock paper allows you to use the same cards year after year.
Put a set of extinction cards into each envelope.

8. Extinction Theories - Lesson Plan

Lesson Plan

Rather than start class with any warm-up or initial discussion, begin by dividing the class into teams and giving each team a copy of the handout. It is important to keep kids from thinking about what they might have heard previously about the dinosaur extinction 65 million years ago. Many have heard about the catastrophic meteor/asteroid/comet theory and are likely to use evidence to justify their previous beliefs than to use evidence to arrive at a theory.
Read through the first page of the handout together, stopping to answer any questions and define any vocabulary the students may be unfamiliar with (mass extinction, theory, etc.).
Emphasize that a theory must be supported by evidence. Encourage students to throw out everything they think they know about the dinosaur extinction and instead seriously consider ANY possible explanation that is suggested by the evidence. The evidence is not equal in importance, so it’s not necessarily the number of evidence cards that matters but the conclusiveness of the evidence that matters. Thus, discourage students from using the strategy of the theory with the most number of evidence cards must be true.
Students may need an example of what a theory looks like, particularly, the way a theory is composed of a series of logically linked statements. For instance, a theory might say “The dinosaurs, and the majority of other organisms that existed at the time, became extinct because space aliens landed on Earth. An alien virus was released, wiping out all the green life forms including all the dinosaurs and plants. This resulted in the collapse of the food web (since all the producers were wiped out) and an increase in the amount of carbon dioxide in the atmosphere (since plants no longer were using carbon dioxide for photosynthesis).”
Once students understand the overall goal of this exercise, give them their cards and allow them to begin. Circulate around the room and help groups that get stuck or cannot agree. Make sure that students do not let their previous assumptions interfere with the process and keep students focused on the evidence cards.
If teams finish early, force them to make their theory as clear as possible and challenge them by pointing out flaws in their logic or evidence that does not fit their ideas. For instance, point out that the Chicxulub crater was formed 300,000 years before the mass extinctions. Force students to think their ideas through completely and explain why they favor some evidence more than others.
The following class period, or when all groups have finished, give each group a chance to present their theory, and their supporting evidence, to the rest of the class. Allow a question and answer period following each group’s presentation. Make sure that questions from other students are also grounded in the evidence and not personal attacks.
When all groups have finished, allow an open debate about the causes of the dinosaur extinction. If necessary, clarify the various theories by writing them up on the board. Use this opportunity to discuss what pieces of evidence are stronger than others and why. If it appears that all teams favor one explanation (as happened in one of my classes), play the devil’s advocate and challenge students with evidence supporting an opposing viewpoint. Always come back to the evidence cards and keep the discussion focused on looking for a theory that best explains the evidence at hand.
10 minutes before the end of class, close the debate and describe the current state of affairs is in the scientific community – that scientists are very divided into the gradualist and catastrophic camps. Allow students to suggest areas of research that could help settle the debate: more conclusive information about how quickly or slowly the extinctions occurred, more clear evidence of asteroid or meteor impacts, more detailed radioactive dating information, etc.

8. Extinction Theories - Going Further

Going Further

Have students research other mass extinctions and compare them to the rate of extinction today. Have students write a position paper arguing whether we are currently in a period of mass extinction or not.
Have students investigate the conflicting theories explaining the Permian extinction, the largest mass extinction known. As they did in this activity, have then summarize one theory about the causes of the Permian extinction and the evidence that supports that idea.

8. Extinction Theories - Sources and Standards

Sources
There are many excellent websites that discuss the K-T extinction:

The UC Museum of Paleontology has a superb discussion of the ongoing scientific debate.
Wikipedia offers a great deal of information about both of the major theories and the evidence in favor of each.
PBS also provides a balanced discussion of the major theories.
Finally, the BBC has a good article about the dating of the Chicxulub crater.

Standards

Field Trip - Caldecott Tunnel

Summary
To apply students’ understanding of the rock cycle and basic principles of stratigraphy, I brought my students to the Caldecott Tunnel to investigate the local geology and piece together the geologic history of their backyard. The east side of the tunnel has an easily accessed road cut that displays a gorgeous example of a contact between older sedimentary rock layers and a more recent volcanic layer. The whole thing has been folded and faulted by the actions of the Hayward Fault, and thus the layers are no longer horizontal but at a sharp diagonal. My students drew pictures of the northern cliff face on the Orinda side of the tunnel then each student was assigned a rock layer to study in detail. When we got back to the classroom, we reassembled the data on the whiteboard, and made theories about the sequence of events that would bring about the rock layers we observed in the cliff. Finally, students drew pictures of what the area must have looked like at different parts of the timeline. This field trip led gracefully into the next segment of the unit on geologic time.

Photograph of the northern roadcut face at the Caldecott Tunnel from the field trip “Caldecott Tunnel between Oakland and Orinda” by Russell W. Graymer in "The Geology and Natural History of the San Francisco Bay Area: A Field-Trip Guidebook", edited by Philip W. Stoffer and Leslie C. Gordon.

Objectives
Can describe the environments in which different sedimentary rocks are formed
Can apply Steno’s 3 laws of stratigraphy to rock layers in the real world
Can apply the laws of stratigraphy to describe the relative age of rock layers, even when the layers have been disturbed
Can use field data to recreate the geologic history of the Berkeley hills
Can make hypotheses about the probable cause of transitions between 1 rock layer and another

Vocabulary
Contact
Stratigraphy
Law of Original Horizontality
Law of Superposition
Law of Lateral Continuity
Depositional Environment

Caldecott Tunnel - Logistics

Time
5-10 min classroom introduction to the field trip
35-45 min collect data at Caldecott Tunnel
travel time varies
45-55 min synthesize data, draw conclusions, and imagine the past through student drawings of the region

Grouping
Individual or in pairs.

Materials

Lab notebooks
Rulers
Optional: hand lenses
Optional: hardness testing materials (penny, butter knife or glass, and steel file)

Setting

Caldecott Tunnel - Background

Teacher Background
The road cut on the east side of the Caldecott Tunnel provides a fantastic example of stratigraphy that students can use to assemble the geologic history of the East Bay Area using their own observations and basic knowledge of geology. Logistically, there is decent parking for a busload of students in the loop of the onramp heading west on Highway 24 from Fish Ranch Road. There is a wide barrier between the freeway and the area to conduct your geologic explorations so you and your students are reasonable safe from the rushing traffic.

North roadcut	South roadcut

As to the geology, the first thing you will notice are clear rock layers at a steep diagonal to the horizontal. Clearly, something happened to turn the originally flat layers, according to the law of original horizontality, on their sides (more on the tilting of the rock layers in a moment). The second thing you will notice are two distinct rock types. As you look at the north face of the road cut, to the upper right are indistinct layers of dark brown rocks while to the lower left are much more clearly delineated grey-green rock layers of an entirely different origin.

Moraga Volcanics	Orinda Formation

Upon closer examination, the dark brown rocks are a volcanic basalt, part of what geologists call the Moraga Volcanics. Their hardness and uniform, microscopic crystallization pattern give these rocks away as igneous rocks. A high iron and magnesium content gives them the distinctive red-brown coloration, as opposed to the more traditional black basalt of other volcanic areas. Among the eroded rock pieces along the base of these volcanics you might also find holey basalt that looks like sea sponge, evidence that some of the basalt contained many gas bubbles that were trapped in the magma as it cooled. There are also great veins of pagioclase crystals that formed as the magma cooled slowly, deep below the surface. The plagioclase was carried to the surface by lava during major eruptions.

The basalt layers are clear evidence that this area was once peppered with active volcanoes. As you look across the highway to the south side of the road cut, the thickness of these lava layers is evident, indicating extensive volcanic eruptions that covered the region in thick lava flows for many thousands of years. Radiometric dating has determined that these Moraga Volcanics are about 10 million years old.

On the other hand, the grey-green rocks are clearly not volcanic. They form easily identifiable layers, alternating between chunky conglomerates, crumbly mudstone, and rough sandstone, collectively known as the Orinda Formation to geologists. These are clearly sedimentary rocks, formed from sediments deposited and then compacted into rock. The conglomerates contain a wide variety of rocks trapped within a matrix of sand and mud. These trapped rocks are rounded and worn, just like river rocks because they are the remnants of an ancient river that once flowed through the area. The sandstones and mudstones are evidence that this river changed over time, changing course so this spot became part of the surrounding flood plain or becoming part of the river delta as sea levels rose and fell. Although these rocks cannot be radiometrically dated, it is clear that the Orinda Formation is relatively older than the 10 million year old Moraga Volcanics that lie on top of them, the law of superposition.

The junction between the Orinda Formation and the Moraga Volcanics is called a contact – a place where 2 distinct geologic formations meet. A close look at the junction between the two layers shows a red layer of mudstone. Unlike the grey-green mudstone elsewhere in the Orinda Formation, the red color is evidence of the mudstone being baked by the red hot lava that flowed across its surface, just as grey clay turns red after it has been fired in a kiln.

To summarize so far, the East Bay was at one time a great river valley with a river coursing through it, changing course and its identity as the ocean levels rose and fell and as sediments from hills being eroded upstream were deposited. Then, 10 million years ago, there was a burst of volcanic activity, flooding the river valley, not with water and transported sediments, but with magma.

So how did these layers get tilted? Sometime after the period of volcanoes marked by the Moraga Formation, the Hayward fault came into existence, causing the Berkeley hills to be pushed upward and the rock layers here to become folded and tilted out of their original, flat orientation. The conglomerates that once lay in a river valley and were then covered in layers of lavarock, were pushed skyward by tectonic forces, lifting them into the cliffs that tower above the roadside today. In the 1930’s construction began on the Caldecott Tunnel proper. As the hillside was cut open and the tunnels bored through the mountains, these beautiful rock layers were revealed.

Student Prerequisites

Crayon Rock Cycle lesson

History of Rock lesson

Layers Upon Layers lesson

Caldecott Tunnel - Getting Ready

Getting Ready

Get permission from CalTrans to take your students to the site. The contact person is Brigetta Smith, CalTrans Public Information Officer, 510-286-5820, [email protected]
You may wish to take the directions detailed in the lesson plan below and print them out as a checklist/handout for the students to carry with them as they complete their observations at the tunnel. I had my students write the general directions in their lab notebooks before departing from the classroom but then realized that many would have benefited from a more detailed checklist.
Each student needs a ruler. Bring a class set or make sure each student brings their own.
Optional: prepare rock study kits to take to the field with hand lenses and hardness testing equipment.
Lay down a strip of masking tape along the wall or the edge of the board as a timeline showing the sequence of events in the formation of the rock layers at the Caldecott Tunnel. The tape should be about 1 foot long for every 2 students in your class.

Caldecott Tunnel - Lesson Plan

Lesson Plan
Classroom Introduction

There are 2 pieces of information that are useful to review with students in the classroom before going on this field trip.
Review the types of rocks students will encounter. This is a good opportunity to take out samples of the rocks and the summary tables created in the History of Rock lesson. Ask students to identify the rocks and describe the depositional environments that created them
Review Steno’s 3 laws. In particular, review how to tell which layer is the oldest using the law of superposition, even when the layers have been tilted.
Describe the observations students will be expected to make at the tunnel and set up the lab notebooks so that students know what they need to do.
Go to the Caldecott Tunnel!

At the Tunnel

Park in the gravel loop within the onramp to the freeway. Gather the students and ask them to look at the north face of the cliff. Have them describe what they notice. The 3 key observations are:
- There are distinct rock layers
- The dark brown rock layers on the top right look different from the light green-grey rock layers on the bottom left
- The layers are NOT flat but tilted
Have students look across the freeway to the south side of the road cut. There, the contact between the dark brown basalt and the gry-green sedimentary rocks is much more obvious. The thickness of the basalt layer is also more distinct. Relate these observations to the rock layers created in the classroom in the Layers Upon Layers lesson. How are they the same? How are they different?
Lead the students across the street, past the base of the cliff, and up a small trail on the left that climbs up to a ledge a little higher up on the cliff-side. Come back along the ledge towards the contact. Here, have kids make additional observations of the rocks layers they see. From this distance, students should be able to observe clear layers within the sedimentary rocks of the Orinda Formation.
Have the students draw a full page picture of the cliff face, paying particular attention to the rock layers they can observe. If the students can, label each rock layer with the name of the type of rock (conglomerate, sandstone, mudstone, basalt, etc.).
On the next page, write a short paragraph describing what you observe about the big picture in words (basically, the 3 key observations from step 1).
As the students finish their drawings and big picture observations, assign each student a rock layer to study in detail. The first student to finish can work on the basalt in front of them. The next can examine the red, baked mudstone. The next can examine the wide conglomerate layer. And so on. If you have more than 20 students, in the interest of time when students are presenting their observations and theories back in the classroom, you may want to have students work on a rock layer in pairs rather than individually.
Each student should draw a detailed picture of their rock layer and the layers that sandwich their layer. They should then make the following observations
- Identify the type of rock
- Measure the size of the grains in your rock in cm
- Measure the width of the entire layer in cm
- Identify the type of rock on either side of your layer - be sure to indicate which one is “above” your layer and which one is “below”
- Propose a theory describing what the area might have looked like before your rock layer existed, what the area looked like during the formation of your rock layer, and what the area looked like after the formation of your rock layer.
A good way to have students confirm their observations and rock identifications is to have them share their observations and theories with the students studying the neighboring layers. They can confirm that they identified the rocks correctly and see if their theory matches that of their neighbors.
Students that finish early can write down their theory of the sequence of events that led to the formation of these rock layers.
Return to school.

Organizing the Data and Drawing Conclusions

Have students open their lab notebooks. Ask them to share their observations and instruct you on how to recreate their big picture drawings on the white board in as much detail as possible. Get them to give you as many details as they can reassemble – the number of rock layers, the type of rock in each, the relative width, etc. Focus on accurately representing the students’ measurable observations. Drawing conclusions about the depositional environment and sequence of geologic events will come later.
When a pretty detailed drawing to work from, begin to reassemble the geologic timeline as the kids see it, starting with the oldest layer that was studied in detail by a student. Of course, that means the students have to decide which is the oldest layer, the sedimentary layers or the igneous layers. Most likely, and correctly, they will select the bottom-most sedimentary layer. Discuss whether these layers were originally laid down at a tilt or if they were laid down flat and then tilted and how they know.
Once you know which is the bottom most layer, each student should have a chance to explain their theory about the environment present at the time their rock layer formed and what evidence they have to support that theory. Keep track of the events on a line drawn across the board with markers for each of the rock layers. As more students present their findings, the presentations will become shorter, leaving time to speculate on how a fast-flowing river might change into a lake or a delta or a sand bank. You could also speculate on the length of time it would take to accumulate each layer of sediments – is it hundreds or thousands of years?
When all the students have gone, there is the remaining problem of how the layers become tilted. Have students propose their theories of what happened to tilt the layers. Most likely, someone will mention earthquakes and propose that the earthquakes folded the rock layers and pushed one end up and the other end down, causing the tilt. The key is to let the students come up with the theory, don’t tell them.
Finally, with the remaining time, I asked each student to create an index card drawing of what they thought that spot would have looked like at the time the rock layer they studied was forming. Imagine standing there thousands of years ago. Would it have looked like a river? Would you have been standing next to a giant volcano spewing hot lava?
Optional: Since there isn’t a “rock layer” that shows the tilting, you might want to draw an index card, or series of cards, showing the hills being pushed up and the tunnel being carved.
Arrange the drawings along the masking tape timeline. You can come back to this timeline, adding additional information (such as the periods and epochs - Miocene epoch 5-24 mya, Tertiary period, Cenozoic era - and the types of plants and animals that might have roamed the ancient river valleys and volcanoes) as students learn about geologic time in the upcoming lessons.

Caldecott Tunnel - Sources and Standards

Sources
The best overview of the geology of the Caldecott Tunnel region is available in the book: The Geology and Natural History of the San Francisco Bay Area: A Field-Trip Guidebook, edited by Philip W. Stoffer and Leslie C. Gordon, published by USGS. The information you want is found in the second field trip, “A Geologic Excursion to the East San Francisco Bay Area”, stop #3, “Caldecott Tunnel between Oakland and Orinda”. The entire guide with other excellent field trips throughout the Bay Area may be downloaded from the USGS website.

Professor Steven Dutch of the University of Wisconsin, Green Bay has put together an excellent series of photos of the road cut near the Tunnel.

To learn more about the Caldecott Tunnel itself, the California Department of Transportation has a website with a historical timeline of the tunnel and information about current projects. In addition, engineers J. David Rogers and Ralph Peck describe the geologic engineering for the BART system (Bay Area Rapid Transit).

For an even broader discussion of the geology in the Bay Area, the USGS has assembled a treasure trove of information about the geology of the San Francisco Bay Area.

Finally, to pan back even further to view the geology of the entire state of California, legendary science writer John McPhee’s book Assembling California provides an in depth, highly accessible discussion of the geologic history of California. READ IT! And read McPhee’s other works such as Basin and Range. I personally disliked geology as a science until I read McPhee and suddenly fell in love with the field.

Standards
Grade 6
Plate Tectonics and Earth's Structure
Plate tectonics accounts for important features of Earth's surface and major geologic events. As a basis for understanding this concept:
e Students know major geologic events, such as earthquakes, volcanic eruptions, and mountain building, result from plate motions.
f Students know how to explain major features of California geology (including mountains, faults, volcanoes) in terms of plate tectonics.

Investigation and Experimentation
Scientific progress is made by asking meaningful questions and conducting careful investigations. As a basis for understanding this concept and addressing the content in the other three strands, students should develop their own questions and perform investigations. Students will:
e     Recognize whether evidence is consistent with a proposed explanation.
f     Read a topographic map and a geologic map for evidence provided on the maps and construct and interpret a simple scale map.
g     Interpret events by sequence and time from natural phenomena (e.g., the relative ages of rocks and intrusions).