Evidence About Earth’s Past (Book)

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RELATIVE AGE OF ROCKS

- Lateral Continuity

Rock layers extend laterally, or out to the sides. They may cover very broad areas, especially if they formed at the bottom of ancient seas. Erosion may have worn away some of the rock, but layers on either side of eroded areas will still “match up.”

Look at the Grand Canyon in Figure. It’s a good example of lateral continuity. You can clearly see the same rock layers on opposite sides of the canyon. The matching rock layers were deposited at the same time, so they are the same age.

Lateral Continuity

Lateral Continuity. Layers of the same rock type are found across canyons at the Grand Canyon.