My Science Box

Getting Ready

1. Make copies of the Earth Journey handout.
2. Make copy of the Earth Journey Teacher Cheat Sheet for yourself.
3. Get sidewalk chalk.
4. Pace out the entire walk to make sure your route is long enough.

Teacher Background
The earth is composed of many distinct layers. Their identity has primarily been inferred from seismic data and from analysis of the magma welling up out of volcanoes. A table of the various layers and a brief description of each follows (this same information is provided on the Earth Journey Teacher Cheat Sheet).

Layer	Actual dist. from center	Description
Inner core	0-1200 km

Time
10 min introduction
35-40 min walk

Grouping
Whole class

Materials

• A copy of the Earth Journey Handout for each student
• A copy of the Earth Journey Teacher Cheat Sheet for yourself
• A piece of sidewalk chalk for each student

Setting
Sidewalk around 2-3 city blocks (640+ meter loop)

Summary
In the style of Jules Verne’s book Journey to the Center of the Earth, take your students on a walk, using sidewalk chalk to mark the boundaries between the different layers inside our planet. After you pass through each layer, tell your students about the layer of the Earth they just traveled through. This lesson was developed by Eric Muller of the Exploratorium Teachers’ Institute. Here you will find a student handout for taking notes during the walk, a teacher cheat sheet and some assessment ideas. Download a detailed lesson plan for this activity from Eric Muller’s website, originally published in The Science Teacher, September 1995.

Sources
Three excellent resources for more information on plate theory include:

Assessment

1. Collect students’ color coded maps.
2. Assign a plate puzzle as homework where students cut out, assemble, and label the Earth’s tectonic plates. My favorite tectonic plates puzzle is produced by the USGS/NPS. (download a copy of the “Plates Puzzle 1 and 2” from the USGS/NPS website under PDF documents).

Color coded and labelled world earthquake map: Original USGS earthquake epicenters map with mid-ocean ridges in orange, volcanic zones in red, and tectonic plate boundaries outlined in blue. See This Dynamic Planet website to download an unlabelled original.

Lesson Plan

Getting Ready

1. Make copies of the “World Earthquake Map” from the USGS/NPS website
2. Make one copy of the Volcano List for each class, cutting them into strips with information about one volcano on each strip.
3. Make a transparency version of the World Earthquake Map.
4. Display the large map with earthquake data already plotted at the front of the classroom.
5. Set out color dots and colored pencils.
6. Print out reference sheets - Earth’s Tectonic Plates and Mid-Ocean Ridges Map.

Teacher Background
As early as the 1920’s scientists recognized that earthquakes lined up along fault zones and were not randomly scattered across the globe. The technology improved dramatically in the 1960’s when standardized seismic monitoring stations were established around the globe to police the ban on above-ground nuclear testing. The location of active volcanoes also lines up along these same zones. For example, the Pacific Ocean is surrounded by volcanoes and earthquake zones – commonly known as the “Ring of Fire”. These zones mark the boundaries of the Pacific Plate. Other tectonic plate boundaries may also be identified in this way.

Yet to see all the borders you also need to look under the ocean. In the late 1950’s, the exploration of the oceans revealed enormous mid-ocean ridges that zig-zag across the ocean floor between continents, nearly encircling the globe in places. These mid-ocean ridges rise on average 4,500 kilometers above the ocean floor and reach peaks higher than most mountains on land. More recent explorations have revealed that the mid-ocean ridges are characterized by huge upwellings of magma similar to volcanoes on land. Incredibly, life, in the form of archaebacteria and other species, exists along the mid-ocean ridges, surviving on the chemicals and nutrients exiting from hydrothermal vents.

Earth's Tectonic PlatesCombining information from all these sources (earthquakes, volcanoes and mid-ocean ridges, it is possible to draw the boundaries of all the Earth’s major plates. The seven largest plates are easily identified: African Plate, Antarctic Plate, Eurasian Plate, Indo-Australian Plate, North American Plate, Pacific Plate, South American Plate. The smaller Philippine and Caribbean plates can be outlined using the prominent volcano and earthquake data. The Cocos and Nazca plates can be distinguished using mid-ocean ridge data.

Only the Juan de Fuca, Scotia, and Arabian plates are easily overlooked. In fact, I generally don’t emphasize these 3 plates if my students don’t identify them themselves since it is not essential to me that they memorize all the world’s tectonic plates, only that they recognize how the crust is broken into moving plates and that they understand how the plate boundaries can be determined with earthquake, volcano and mid-ocean ridge information.

Several critical questions remain:

• Why are there earthquakes, volcanoes and ridges at the plate boundaries?
• How come you don’t see earthquakes at the midocean ridges so much?
• Why are there earthquakes but not volcanoes in the Himalayas above India?

All these questions are related to the differences in what is happening at each of the plate boundaries. (I choose to hold off on discussing these issues with my students until after they learn about the interior of the Earth, convection cells, and sea floor spreading.)

Plate boundaries may be divided into 3 main categories: convergent boundaries where plates collide, divergent boundaries where plate pull apart, and transform boundaries where plates grind past each other. Convergent boundaries in turn have different characteristics depending on if it is 2 pieces of continental crust colliding (continent-continent convergent boundary) or if 1 piece of oceanic crust is diving down below a piece of oceanic or continental crust (subducting convergent boundary).
Types of plate boundaries: Image courtesy of the USGS.

• With divergent boundaries, like the mid-ocean ridges, Iceland, and the African rift valley, you get few earthquakes because the plates are pulling apart, not storing up energy as they collide or rub past each other. Instead, a gap forms between the plates and magma is pushed up from the mantle below to fill in the hole. Thus, you get lots of volcanoes, thermal vents, and great broken rifts in the earth.
• With transform boundaries, like the San Andreas fault (most of other transform boundaries lie on the ocean floor), you get lots of earthquakes and only occasional volcanic activity. The plates are moving past one another and storing energy between them until the friction holding them together gives way in the form of an earthquake.
• With subducting convergent boundaries, as in the northwestern edges of the Pacific Plate, the west coast of South America, and the northeastern edges of the Indo-Australian Plate, you get a combination of volcanoes and earthquakes. The lighter plate floats on top while another plate dives below the edge in a process known as subduction. As this occurs, the submerging plate melts and bubbles up through cracks in the overlying crust as volcanoes.
• With a continent-continent convergent boundary, like the Himalayas at the boundary between the Indo-Australian and Eurasian plates, you get lots of earthquakes but very little volcanic activity. That is because both continental crusts are light and resist subduction. Instead, they buckle and crumple against one another, gradually rising skywards inch by inch. In fact, the Himalayas continue to rise at the rate of approximately 5 mm a year.

For ways to model these different plate boundaries with students, see the Sea Floor Spreading activity.

Time
20-30 min add volcano data to map
20-30 min learn about mid-ocean ridges and add them to the map
45-50 min trace and color code plate boundaries and label with the names of tectonic plates

Grouping
Individual

Materials