The Earth's History — Test

Question 18 • Earth and Space Science

How can varves be used to construct a timeline of environmental changes?

Answer

Varves can be correlated between distant locations to provide a continuous record of climate change throughout Earth's history.

Varves record annual freezes and thaws and contain bubbles of air that can tell us about how the atmosphere changed.

Varves contain radioactive isotopes that decay at a steady rate and can be used to determine the relative ages of sediment layers.

Varves record seasonal deposition of sediments in glaciers and lakes and contain pollen that tells us about past environments.

Explanation

Varves are thin sediment layers deposited in repeating seasonal cycles, often one pair of layers per year. Their composition and preserved pollen can reveal changes in vegetation and other environmental conditions over time, allowing scientists to build a timeline. The air bubbles in choice C are associated with ice cores, not varves.

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