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| It
is possible to reconstruct an |
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| approximate
chronology of the |
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| ice
ages by measuring the |
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| oxygen
isotopes in ocean |
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| sediment
cores. As marine |
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| organisms
perish, their |
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| skeletons
are deposited on the |
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| bottom
of the sea floor. The |
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| layers
of deposited skeletons |
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| provide
information about |
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| climate. |
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