Summary
What's the big deal about rocks? They don't move, aren't flashy, and seem pretty useless to the untrained eye. To discover the beauty of rocks, one must look closer and learn how to read them. 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
Sedimentary rock
Erosion
Sediment
Cement
Lithifaction
Metamorphic rock
Igneous rock
Magma
Rock cycle
Attachment | Size |
---|---|
rock_cycle_handout.doc | 27.5 KB |
1rock_cycle_v2.doc | 69.5 KB |
Time
45-50 minutes
Grouping
individual
Materials
Each student needs:
For the whole class:
Setting
classroom
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:
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”.
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.
Getting Ready
Lesson Plan
Assessment
Going Further
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.
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:
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.
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
Attachment | Size |
---|---|
rock_data_sheet.doc | 20 KB |
2compare_rocks_v2.doc | 73 KB |
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
Setting
Classroom
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.
Getting Ready
Lesson Plan
Basalt | Granite | Mudstone | Sandstone | Conglomerate | |
Type | |||||
Color | |||||
Texture | |||||
Grain Size | |||||
Crystal Size | |||||
Layering | |||||
Hardness | |||||
Environment |
Assessment
Match each statement to the type of rock being described:
a) sedimentary
b) igneous
c) metamorphic
______ 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
Sources
Many rock identification guides are available on the Internet. My favorites include:
For more information about mineral testing, including using the Mohs scale of hardness, see:
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.
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.
Summary
The study of rock layers, or stratigraphy, is a natural way to introduce students to the fundamental principles of geology and to lead into the idea of geologic time. In this lesson, students are introduced to Nicolas Steno’s 3 major laws of stratigraphy: the law of original horizontality, the law of superposition and the law of lateral continuity. Students also add their observations of sediment sorting from previous lessons (Soil Analysis, Erosion Patterns, and the Sediment Study Project) to generate a fourth “law” concerning depositional environment – the tiny grains in mudstone were most likely deposited in very still water like a lake or delta while large gravel in conglomerate was most likely deposited in fast moving rivers and streams. While this activity has students depositing sediments in clear plastic cups or Mason jars, it is recommended that the teacher simultaneously conduct the activity using a squeeze box like the one described by Eric Muller. In this way, when the student activity concludes, the teacher can take the activity further to show how layers can become folded and faulted by plate movements. This lesson is a natural extension of the Going Further activity from the Crayon Rock Cycle lesson where sediments are mixed with sodium silicate to create home-made sedimentary rocks.
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
Attachment | Size |
---|---|
layers_upon_layers_v2.doc | 69 KB |
Time
45-50 minutes
Grouping
Individual, although clusters of 4-6 students need to be able to share materials
Materials
Setting
Classroom
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 original horizontality states that when sediments are deposited, they settle in flat, horizontal layers. The layers are level like a floor. When students conduct the activity and add the first layer of sediment, they will observe that the sediments drift down through the water and come to rest as a flat layer on the bottom of their cup. Similarly, on the sea floor or bottom of a lake or in a delta, sediments will settle due to gravity in a flat layer.
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).
Getting Ready
Lesson Plan
Assessment
Going Further
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:
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.
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.
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.
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
Attachment | Size |
---|---|
4my_time.doc | 50.5 KB |
my_time_handout.doc | 37.5 KB |
Time
45 minutes
Grouping
Individual
Materials
Copy of the Personal Time Scale handout for each student
Setting
Classroom
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.
Student Prerequisites
None, although exposure to Steno’s law of superposition and experience relating rock layers to relative time will help students understand why they are doing this activity in the context of geology.
Getting Ready
Make copies of the Personal Time Scale handout.
Lesson Plan
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.
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.
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
Attachment | Size |
---|---|
geologic_time_web.doc | 23 KB |
5geologic_time_v2.doc | 56 KB |
Time
45 minutes
Grouping
Individual, although pairs of student sharing a computer also works well
Materials
Setting
Classroom or computer lab
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.
Getting Ready
Lesson Plan
Going Further
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:
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:
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.
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
Attachment | Size |
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geologic_time_handout.doc | 49 KB |
6geologic_timelines_v2.doc | 68.5 KB |
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
Setting
Classroom
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 reflect 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.
Getting Ready
Lesson Plan
Geologic time as a calendar year:
Geologic time as the distance from Los Angeles to New York City:
Assessment
Going Further
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:
For more information on the geologic time scale, see:
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.
b. Students know the history of life on Earth has been disrupted by major catastrophic events, such as major volcanic eruptions or the impacts of asteroids.
d. Students know that evidence from geologic layers and radioactive dating indicates Earth is approximately 4.6 billion years old and that life on this planet 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.
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
Can list the different types of fossils and the way each forms.
Can describe and diagram the conditions required for the formation and discovery of fossils.
Can understand why fossils are so rare and why many forms of life that once existed on Earth have not yet, and may never be, discovered.
Vocabulary
Fossil
Body fossils
Permineralization
Trace fossils
Mold fossils
Cast fossils
Attachment | Size |
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fossil_adventure_pages.doc | 34.5 KB |
7fossil_adventure_v2.doc | 63 KB |
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
Setting
Classroom
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:
Due to the rarity of fossils, the buying and selling of fossils has become a highly controversial subject. Paleontologists are concerned that the commercial fossil trade is harmful to science. Scientists fear that if unique fossils with great scientific importance are purchased by private collectors, then these finds may not be available for scientists to study. On the other hand, private collectors insist that most fossils are being made available to researchers and many are ultimately donated to museums. For a great video discussing the subject, see “Curse of T Rex”, a 1997 Nova special about the discovery of an astonishingly complete T rex skeleton (Sue, now on display at the Field Museum (http://www.fieldmuseum.org/SUE/)) and the battle that ensued between scientists, commercial fossil hunters, the US government, and property owners.
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.
Getting Ready
Lesson Plan
Assessment
____ 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!
Going Further
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:
For pictures of fossils, see:
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.
Summary
Cartoon by Chris Madden
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
Attachment | Size |
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8extinction_theories.doc | 63 KB |
extinction_handout.doc | 33.5 KB |
evidence_cards_v2.doc | 47.5 KB |
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
Setting
classroom
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:
Yet, even with an abundance of evidence, there is no consensus among scientists as to what happened at this time. Generally speaking, scientists are divided between two camps:
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.
Getting Ready
Lesson Plan
Going Further
Sources
There are many excellent websites that discuss the K-T extinction:
Standards
Grade 7
Earth and Life History (Earth Sciences)
4. 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.
b. Students know the history of life on Earth has been disrupted by major catastrophic events, such as major volcanic eruptions or the impacts of asteroids.
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.
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.
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
Attachment | Size |
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trip_caldecott_v2.doc | 67.5 KB |
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
Setting
Part 1: Caldecott Tunnel on Highway 24 at Fish Ranch Road
Part 2: classroom
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 |
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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 |
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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
Essential to this field trip are: a solid understanding of the rock cycle (see Crayon Rock Cycle lesson), previous experience identifying the individual rocks that will be encountered in the field and deducing the history of their formation (see History of Rock lesson), and a good grasp of the major principles of stratigraphy (see Layers Upon Layers lesson).
Getting Ready
Lesson Plan
Classroom Introduction
At the Tunnel
Organizing the Data and Drawing Conclusions
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.
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.
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.