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How do we know what Earth's climate was like long ago?

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We Asked a NASA Scientist.

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Earth's climate affects almost everything.

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And so when the climate changes, it leaves traces almost everywhere.

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Some of those traces can be seen in the landscape —

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erratic rocks that have been pushed far from their origin by ancient glaciers,

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or relic beaches that tell us how high sea level was in the past.

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Other traces are more subtle —

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the composition of ice in cores drilled in Greenland and Antarctica,

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or the geochemistry of the shells of single-celled organisms in ocean sediment

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that can date back hundreds of millions of years.

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These efforts have led to detailed understanding of the ice ages of the last

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few million years and the hothouse climates of 50 or 100 million years ago.

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They've given us insight into long-term changes driven by plate tectonics,

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shorter-term variability driven by the wobbles in the Earth's orbit, and rapid events

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such as the climate response to the
asteroid impact that killed the dinosaurs.

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And they've allowed us to see that what's happening to

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climate right now is unlike anything else we've seen.

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So how do we know what Earth's climate was like long ago?

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The answers are all around us

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if we know where to look.

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We Asked a NASA Scientist.