Evolution of the early Earth

There are two important ways to think about impact frustration in the evolution of life on Earth:

(a) Impacts halted the origin of life before it could firmly take hold

(b) Impacts affected which organisms survived, i.e., affected the course of evolution on Earth

We know that (b) occurred 65 million years ago when the dinosaurs were wiped out (we will talk about this more next month).

We suspect that (b) occurred something like 3.8 billion years ago -- give or take some unknown but important amount -- from our Last Common Ancestor, the thermophile.

Some people suspect -- it will be impossible to prove -- that (a) also occurred on Earth, perhaps many times. Think of a well-placed impactor landing in our carefully constructed somewhat quiescent mineral-rich pond....

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