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What was the climate like 18,000 years ago? Amazingly, scientists actually know.
They’ve gathered clues from rocks, fossils, ancient ice, and ocean sediment and put them together to form a picture of the last great ice age, when glaciers pushed down into what is now the United States.
Scientists can go a lot further back than that, though. Using similar clues, they’ve tracked rising and falling global temperatures over the past billion years.
