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Impact hypothesis

Seth Ellestad wrote:

>Well, it seems that impact crater or not (what else COULD something like
>that be?) dinosaurs existed through many such events---in the Triassic and
>Jurassic as well.  Perhaps it was not the trigger for the extinction of
>these animals, as many already argue, perhaps if it was, it just chanced to
>hit at a particularly inopportune time when the number and viability of
>species was in a downturn.  And whereas perhaps impacts may have served as
>events to trigger evolutionary spurts before, at that particular time it
>just added too much more stress to an already [at the time] particularly
>stressed group of animals and "broke the camel's back".

One idea I've seen kicked around is that perhaps our solar system wandered
into a region of greater spatial density a few million years ahead of the K-T
line. The solar system of course moves in an orbit around the center of the
Milky Way Galaxy, requiring about 250 million years to make one circuit. This
might have reduced temperatures globally and perturbed a lot of asteroids so
that they collided with the moon, Mars, Earth, and other planets. Perhaps the
dense cloud the solar system might have passed through contained asteroids
and cometary nuclei which rained down on Earth for several million years
ahead of the really big whammy in the Yucatan. Some point to the apparent age
of some prominent lunar craters (such as, if I recall correctly, Copernicus -
about 70 million years old) as "evidence" for this notion. It's all very
speculative, but might provide an explanation for the gradual tapering off of
dinosaurs ahead of the K-T boundary. Generally bad astronomical weather
stressed the dinosaurs and other species, and one more big whammy "broke the
camel's back." 

David Portree