- from Climate
Amazingly, scientists actually know what the climate was like 18,000 years ago. They have clues from rocks, fossils, ancient ice, and ocean sediment.
Together, all this information created a picture of the last great ice age. That was when glaciers pushed down into what is now the United States.
That’s not even as far back as scientists can go. They’ve actually tracked changes in global temperatures over the past billion years.