So I know that the 5th one wiped out the dinosaurs. But how do we know of the other 4 before that, and how did we figure this out? What kind of life was on earth before the extinctions?
In: Planetary Science
The rock near the surface of the Earth occurs in layers, with newer rock appearing over older ones. We can examine these layers of rock to determine their age. We can look at their composition to learn things about the Earth at that time. We can look at fossils in those layers to learn about life at that time.
It takes a lot of combining of evidence across many different observations to get a clear picture and, of course, there’s still a lot we don’t know.
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