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New extinction theory

Re: the notion that a near-miss by an asteroid could make the Earth wobble -

This is not possible. There are no bodies of sufficient size in
planet-crossing orbits, nor any evidence that there were any as recently as
65 million years ago. 

The typical asteroid (5 km wide) could skim Earth's atmosphere with no effect
on our planet's tilt or day length. Even the largest asteroids (500 km wide)
are negligible in mass when compared to Earth. 

If an asteroid is going to play a role in extinctions, it must strike Earth.
Even then it would have no appreciable effect on spin or tilt.

To affect spin or tilt, a body nearly as massive as the moon (1800 km wide -
1/80 Earth's mass) must strike Earth. This would strip away the crust and a
large part of the mantle. If this happened, then changes in spin and tilt
would probably result from the reconstitution of our planet from outflung
debris. But there'd be no life left to be bothered by the resultant changes
in lighting conditions.

David Portree