Question

1. How many ice ages do scientist estimate have occurred during the last billion years?

A) 3
B) 5
C) 6
D) 7
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2. How often do scientists say that recent cycles of advancing and retreating ice sheets occur?

A) approximately every 100,000 years
B) approximately every 50,000 years
C) approximately every 10,000 years
D) approximately every 1,000 years

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3. Which is faster: the advance or the retreat of an ice sheet?