this post was submitted on 12 Jul 2023
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[–] sjh@sh.itjust.works 9 points 1 year ago (1 children)

Curious: how do they know that? Recorded history is like 5k years right?

[–] UhBell@lemmy.world 25 points 1 year ago (1 children)

Scientists use climate proxy records like coral skeletons, tree rings, glacial ice cores, and sediment layers. For example, the levels of oxygen 16 in a layer of ocean debris and fossils go up as temperatures rise. So a high level of oxygen 16 in sediment from one layer tells scientists that the planet was hot and watery when the sediment was laid down.