Science, Earth and Space Science

Grade 5- 8

Objective

Students will be introduced to the topic of Earth's crustal plates and how their motion has changed the surface features we see today.

Directions

Background
Scientists have gathered evidence which shows that the Earth's crust is broken into sections, much like the cracked shell of a hard-boiled egg. The crust is actually very thin compared to the rest of the Earth. If the shell were removed from the hard-boiled egg and the egg sprayed with paint, the thin layer of the paint would closely resemble the depth of the crust relative to the internal sections of the planet.
When equipment made it possible to map the ocean floor and dive to the great depths, another world opened to scientists. High ridges and deep trenches were discovered on the ocean floor. Molten lava was seen pouring from cracks in the ocean floor. This added to the knowledge of the Earth's crust and helped support the theory of Continental Drift. The crust is constantly being recycled as new, molten material rises through cracks and pushes aside old material before solidifying.
Edges of some of the crustal plates are diving beneath others, creating earthquakes and volcanic activity. An example of this is the Pacific Plate. The collision of these plates also causes uplifting of mountain ranges. This can be seen along the western edge of South America as the Nazca Plate pushes under the South America Plate, lifting up the Andes Mountain range along the coastline.
As a plate dives beneath another, it begins to melt down when it comes in contact with the hotter mantle lying under the crust. The result of all this is the slow but continuous recycling of the Earth's crust, continents relocating, and mountains rising.
Preparation

• Make copies of Earth's Plates Puzzle and cut the pieces apart. Put the pieces for each puzzle in a separate envelope. Make a transparency of this page and cut them apart.
• Hard-boil an egg, crack the shell in several places, and then outline the edges of these cracks with permanent black-felt pen.
• Display the maps in the classroom.

• Show the students the hard-boiled egg with the cracked shell. Explain how it is like the crust of the Earth (see Background).
• Show the students The Earth's Fractured Surface map. Point out the ridges and trenches in the ocean floor which form the boundaries of the crustal plates.
• Use the background information from page 68 to describe what happens as these plates push against each other.
• Divide the students into small groups and give each group an envelope with the Earth's Plates Puzzle pieces. Have them put the puzzle together, using a world map to assist them.
• Distribute the data sheet to each group for them to complete.
• Provide for the students reference books which will help them answer the information on the data sheet.

Resources

• transparency of Earth's Plates Puzzle (page 70--see link below)
• sets of Earth's Plates Puzzle cut into puzzle pieces
• map of Earth's plates
• large world map
• Plates on the Move (page 71--see the link below) data sheet
• hard-boiled egg
• overhead projector