The next subject students tackled was isostasy. They used a large container of water to model the asthenosphere, the upper layer of the Earth's mantle on which the lithosphere floats. Blocks of styrofoam and wood represented continental lithosphere, sponges represented the oceanic lithosphere. In the image to the left, two pieces of continental lithosphere collide to form a mountain belt.

To the left, the more dense oceanic lithosphere (represented by the sponge) collides with, and subducts beneath the more buoyant continental lithosphere (represented by the styrofoam.) To the right is a Fig Newton which is also an excellent model of the uppermost layers of the Earth. The cookie part represents the rigid, stony lithosphere. The jelly part represents the plastically flowing asthenosphere. When students subjected the Fig Newtons to divergent or convergent stresses, the cookie part cracked, while the jelly part flexed or flowed (this works best when the cookie is warm.)

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