Bug Squash posted:

I don't think I disagree with anything you just posted, my issue is with the claim that the giant impact, assuming it happened, is nessesary for a magnetic field to form on a rocky planet, for the reason that the planet would be solid otherwise.

The fact that Venus has a liquid interior, but no evidence of a giant impact, seems to break this chain of reason.

(Note that Venus doesn't have a strong magnetic field due to how slowly it rotates and some other effects. I think this is irrelevant to the discussion, but feel free to disagree)

(Also, it could be that giant impacts are actually common but usually leave no evidence and earth is only odd in that it got left with a big mood. If that's the case then it's just part of normal planetary formation and doesn't have much to say about how common life is)