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New extinction theory redux



Stan Friesen wrote:

>>On the other hand, an off-center *impact* might well have that as
one of its side effect.  The force generated by such an event is
prders of magnitude larger than the gravitational effects. And if
the force vector were oriented correctly relative to the rotational
axis, it could have substantial effect on the rotation.<<

There's a misconception about relative sizes and scales going on here. An
off-center impact on Earth by an asteroid would *not* affect rotation. An
off-center impact of an asteroid on another asteroid (or small moon) probably
would. Planets are not billiard balls clicking together on a table.

Planets are big but also soft - it you put Earth on a big flat floor
(assuming you could find one) under one gravity of acceleration, it'd sag
into a puddle. When you hit a planet with an object large enough to affect
spin and tilt - it would, BTW, have to be much bigger than an asteroid - you
disrupt the planet. However, the planet doesn't fly apart - it goes into
orbit around itself and eventually re-coalesces. The "new" planet would
almost certainly have a new spin and tilt, but it would also have a new
atmosphere and any water it started with would be gone. Such impacts have not
occured for about 4 bilion years - since the solar system was undergoing
final accretion.

To put the discussion back in the context of paleo, asteroid impacts - which
have left millions of round scars all over the solar system - are not even
"noticed" by the rocky component of a planet. Only when we tighten our focus
onto skinny little atmospheres and the thin film of biota on Earth do the
effects of asteroidal impactors become impressive. And these effects are,
IMHO, sufficiently impressive on that scale to account for major extinction
events without invoking improbable changes in spin and tilt.

Sorry to get off topic - I feel the same obligation to correct misconceptions
that many on this listserve might feel if an astronomer got on and wrote that
tyrannosaurs ate apples. <G> 

David Portree