I read something similar years ago... idea being that big insects (huge dragon fly's n stuff) were only able to exist in high o2 conditions because they breathe thru their skin holes.... the idea was that the reason they didnt return after birds appeared was that birds thought they were tasty and had the jump on them evolutionarily speaking
But you are also missing that the tilt of the earth meant that an impact probably pushed it out of its prior orbit. This probably also caused gravitational changes and what not.
Pretty sure that an impact that could knock the earths orbit out would have had such energy as to turn the surface into molten liquid and kill every life form upon the earth.
The only time anything that big is suspected of hitting is when the moon was created way way way before life on th eplanet.... but hey, I dont know everything and its been a while since I read up on the subject. As far as I know the tilt moves thru procession from the slight wobble, and even tree growth and ice formation can have a small effect on it... times that by millions of years and its a real effect.
Man I miss playing Sim Earth from my Dos PC days... you could tilt the planet and have one side ice and the other desert
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