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Re: Asteroid impact finally confirmed?



Firstly to disagree with your subject. It wasn't a case of "finally
confirmed" - the impact has been known and accepted for a long time.
What it
did do was strengthen the link between the impact and the extinction.
The
trouble had been the the KT boundary had only been seen in low
resolution -
the whole period represented by only 1cm or so, so you get lots of
fossils
at the bottom, a thin smear of iridium clays and glass and then
another lot
of fossils straight afterwards with a differing species distribution.
Whats
different for these cores is that the 'thin smear' is expanded up to
around
10cm, and we can clearly see that what looked like an instant
resumption of
life with differing species present was actually a significant period
of
sparse life followed by a slow buildup of certain surviving phyla.
That is a
tighter causal link between the impact and the extinction than we had
before.

Jonathan Woolf wrote:

[snip]

> I've wondered more and more about the "asteroid impact" theory over the
> past year or two.  I don't think it makes a whole lot of sense.  The
> general outline hangs together, but one simple question still lacks an
> answer. Very simply, if this asteroid-induced holocaust swept the world,
> reached every continent and every corner of the ocean, wiped out
> dinosaurs, mosasaurs, pterosaurs, ammonites, etc., _everywhere_, with 100%
> success -- then how did anything survive at all?

It sounds like you are envisioning the day of the impact as being the
cause
of the wipeout. Sure maybe continents-worth of creatures got wiped out
in
the firestorm, but the main killer would be the century or so of low
light
and wintry conditions that having a dust-laden stratosphere would
cause.
Certain plants would die completely, surviving only as seeds in the
ground.
Others would become dormant, not fruiting or flowering. The creatures
that
depended on these plants for food or shelter would perish with them.
Certain
turtles today cannot breed if the summer temperature drops below a
certain
value. they would be wiped out in a single generation in a 'dark
winter'
that caused climate change. Sex distribution in offspring of
crocs/alligators is detemined by incubation temperature: maybe certain
dinosaurs died out because their last generations were 90% male. These
are
just a few possible mechanisms. The general point is that the most
successful organisms tend to be the most highly adapted to their
specific
environment (leaving intelligence out for a moment). If that
environmental
niche changes significantly, those adaptations become a liability. The
less
niche-specific generalists that scrape a living at the edges during
'normal'
times come into their own at that point, able to exploit the new
environment
in ways the others can't. It becomes a race to find who can cling on
long
enough to adapt to the new conditions, and how successful you have
been up
until that point has no bearing on how well you will do in this
particular
contest...

> Can anyone offer a possible reasonable answer to this?

Thats my take, above.

M.


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