A few years ago the movie Water World was playing to large audiences. However, Earth will never be a true Water World. Even if the ice caps melt, sea level would rise "only" a few hundred feet. It would be a disaster, but any place more than 300' above sea level now would remain as dry ground. But, why is this so? What is special about the continents that make them rise above the oceans? After all there must be a reason, and as scientists, it is our responsibility to ask that kind of question and to try to discover the answer.
 
 

I. A second look at the hypsographic curve.

A.  Summary of Earth's topographic relief

B. Bimodal distributions

C. The rocks of continents and oceans

II. The structure of Earth

A. Physical layers and their properties
    -- Plastic vs. brittle behavior

B. Chemical layers and their properties

C.  Examples of crust and mantle

III. The response of plastic rock to floating objects.

A. Experiments with wood and water

B. Thought experiments with plastic rock and crustal block

C. Conclusion and Implication

Objectives/Questions

1. Discuss the bimodal nature of the Earth's crust and relate that to chemical and physical differences of the crust of continents and ocean basins.
 
 

2. Describe the differences that produce the crust and mantle and that produce the lithosphere and asthenosphere.
 
 

3. Describe the response of the lithosphere to a stress like a large additional mass at the Earth's surface and the response of the asthenosphere to a similar stress.
 
 

4. You are presented with the following problem: You are shown a photo of two blocks of identical material floating in water but are not able to see the blocks below the water line. One block's upper surface is 2 inches above water. The other block's surface is one inch above water. Assuming both blocks are rectangular prisms and both are made of the same material, how do they look below the water line?
 
 

5. The drawing above shows the upper surface of the Earth. Draw the lower surface of the Earth's crust at its contact with the mantle.

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