>> “A meteor/comet that large would punch a large hole in the ozone, and allow the atmosphere to escape into space.” <<
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A meteor would cancel the gravitational field of the Earth?
That doesn’t even rise to the level of good SciFi.
There are rocks on the moon that came from Earth, and vice versa. How do you think that happens?
A large meteor entering the atmosphere at 20,000 mph is going to heat the atmosphere, and the expansion will cause some of it to escape, and the outlet is the nearest hole, which the meteor just punched through our protective layers.
If you take away the protective layers above the Earth, it is well understood that the atmosphere will float off into space. Look at the moon. It has no protective field, and it has no atmosphere.
Cause and effect, no?