13. Glacial periods

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Glacial periods are periods in the Earth's history where the climate became cooler. Interglacial periods are periods in Earths history where the climate became warmer. The earth alternates between the two periods every 100,000 years. An example of a glacial period would be the last Ice Age. The last Ice age peaked around 16,000 BCE, and lowered temperatures around 65 degrees fahrenheit. Glacial and Interglacial periods change the organisms and ecosystems around them. For example, many large animals in North America became extinct due to the period changing to an interglacial period.

         -Will Leger

Manual page 31

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