Explain why the two elevations, around 0.5 kilometers above and ...

[Melani1276]

Explain why the two elevations, around 0.5 kilometers above and 4.5 kilometers below sea level, are the most common elevations on Earth.
 
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Question 2

What evidence did the most recent ice age provide us to evaluate the merits of the Pratt-Airy isostasy and flexural isostasy models?
 
  What will be an ideal response?

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Answer to Question 1

The two common elevations represent the two types of crust on Earth. Continental crust underlies most of the area at 0.5 km above sea level and oceanic crust underlies the area at 4.5 km below sea level. Continental crust is thicker and less dense than oceanic crust and so it sits up higher in the mantle, averaging 0.5 km above. Oceanic crust is more dense and thinner than continental crust, so it sits lower in the mantle, averaging 4.5 km below sea level.

Answer to Question 2

Both models require that the crust subside due to the weight of the glacial ice. The Pratt-Airy model requires that only the crust beneath the glaciers subsides and the crust adjusts rather quickly as the ice melts and would be completely adjusted after all the ice is gone. The flexural model requires that an area larger than the area covered with glacial ice will subside and that the adjustment to the melting of the ice will be slow. Data supports the flexural isostasy model because areas larger than those covered by ice are still undergoing isostatic adjustment today.

[Melani1276]

Gracias!

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