> <<"It is also probable that many of the other mass extinctions that were
> thought to have taken place during the history of life on Earth either
> not happen or have been greatly exaggerated.">>
> Don't we have a layer of iridium lined throughout much of the world, that
> cannot be explained via volcanic eruption/deposition? Plus, there is the
> cratering that nicely, fits in with the Yucatan penninsula. And that fits in
> with the creation, via hydrostatic shock, of the Deccan Traps in India.
> Where are the descendents of the dinosaurs, then-just birds? No
> broto-juniors, no giant nautilus, washing up on our beaches, ruining surfing
> events? Feh! What about the Permian (non?) Extinction, of 250 million
> years ago?
Just because an impact happened doesnt necessarily mean that it wiped
out the life forms directly, and fossil deposition is a tricky business
For example, it is now conclusively shown that the West Antarctic Ice
Cap has been stable for at least the last 15 million years, withstanding
global temperature changes as much as 4 deg C warmer than present levels
without any collapse. Despite this, there are plateaus of wave action
sedimentation on the continent with fossilized birch roots that date to
only 4.5 million years that would seem to indicate that not only was sea
level higher significantly at that point, but that Antarctica was
significantly warmer than at present, enough to collapse the ice cap
(birch trees require summer temps of at least 5 deg C to survive).
Rather, it is more probable that the birch roots arrived via ocean
currents and tsunami action, as the circumpolar currents did not become
fully established until 4.5 million years ago..
This archive was generated by hypermail 2b30 : Sat May 11 2002 - 17:44:20 MDT