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Isostasy
Chpt. 4 Test is on Friday, Nov. 20
Isostasy
 This theory states that Earth’s lithosphere
floats on a plastic-like part of the mantle
(asthenosphere).
Earths Crust
 Earth’s crust is thicker under mountains. As
mountains get lifted higher, the crust
becomes thicker and extends further down
into the mantle.
 When mountains start eroding, the erosion
lowers the mountain and the crust rises
back up because the weight has been lifted.
How old is a mountain?
 Rugged, tall mountains are normally
younger than rounded mountains.
– Why is this a sign?