Twig 4th Grade Mod 3 Review

The rocks at the bottom of the Grand Canyon are the oldest.

The Grand Canyon

This layer is about 515 million years old. Sediment was brought here and deposited.

This layer was underwater. Many animals lived in this sea.​

Changes to the planet can be quick, deadly, and catastrophic or slow and unnoticeable

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Definition

the process of wearing or being worn by long exposure to the atmosphere.

Definition

the process of eroding or being eroded by wind, water, or other natural agents.

When the glaciers pushed on the sandy surface, it left some water behind it. It also pushed the sand around it. It disturbed the land. It also pushed a lot of the sand to the front. This is modeling SEDIMENT. Water carries SEDIMENT down. It can also collect it too and not stay plain.

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Erosion can take millions of years to see the change. No human has ever witnessed it happening.​

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Erosion

Erosion and changes are also affecting manmade structures. The Great Wall of China is one example. Naturally, the wind and rain erodes part of it. But can humans do to change it?