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(WA) One reason oceanographers analyze1 the sediment2 on the ocean floor is to see how long-terms changes in Earth's temperature have affected3 the depth of the ocean. By analyzing4 the remains5 of sea animals in old layers of ocean sediment, oceanographers can determine the depth of the ocean in the past. They've analyzed6 hundreds of such layers, including some from the coldest periods of Earth's history --- the ice ages. What they've found is that during the ice ages, the amount of water in the oceans decreased. Water levels in the ocean dropped by about four hundred feet. Water from the ocean evaporated and became frozen in continental7 glaciers8, so it didn't drain back into the ocean. When temperatures eventually rose again, the glaciers melted, and the oceans returned to their former depths. Analysis of sedimentary data indicates that periods of glacial freezing and melting occurred in regular cycles of twenty thousand, forty thousand, and one hundred thousand years.本文本内容来源于互联网抓取和网友提交，仅供参考，部分栏目没有内容，如果您有更合适的内容，欢迎 点击提交 分享给大家。
