This is another press release for the soon-to-appear
paper from the group that proposes a late Holocene
impact over North America 12,900 years ago. Even
though it's only a press release, it does clear up one
detail, though.
As has been pointed out on the List by those following
the issue, the black mat layer took a long time to deposit,
hence could hardly be itself a marker of an impact, which
is a sudden event. Well, this press release makes clear that
the various ET markers of an event were all found UNDER
the black mat layer.
That, at least, makes more sense.
Sterling K. Webb
Full text follows:
http://www.sciencedaily.com/releases/2007/09/070924172959.htm
Extraterrestrial Impact Likely Source
Of Sudden Ice Age Extinctions
At the end of the Pleistocene era, woolly
mammoths roamed North America along with a
cast of fantastic creatures -- giant sloths,
saber-toothed cats, camels, lions, tapirs
and the incredible teratorn, a condor with
a 16-foot wingspan.
About 12,900 years ago, these megafauna
disappeared from the fossil record, as
did evidence of human remains. The cause
of the mass extinction and the human migration
is a mystery. Now a team of scientists,
including Brown University planetary geologist
Peter Schultz, provides evidence that an
asteroid impact likely caused the sudden
climate changes that killed off the mammoths
and other majestic beasts of prehistory.
In the Proceedings of the National Academy
of Sciences, the international team lays out
its theory that the mass extinctions in North
America were caused by one or more extraterrestrial
objects -- comets or meteorites -- that exploded
over the Earth or slammed into it, triggering
catastrophic climate change.
The scientists believe that evidence for
these extraterrestrial impacts is hidden
in a dark layer of dirt sometimes called
a black mat. Found in more than 50 sites
around North America, this puzzling slice
of geological history is a mere three
centimeters deep and filled with carbon,
which lends the layer its dark color. This
black mat has been found in archaeological
digs in Canada and California, Arizona and
South Carolina -- even in a research site
in Belgium.
The formation of this layer dates back 12,900
years and coincides with the abrupt cooling
of the Younger Dryas period, sometimes called
the Big Freeze. This coincidence intrigued
the researchers, led by Richard Firestone of
Lawrence Berkeley National Laboratory, who
thought that the black mat might be related
to the mass extinctions.
So the researchers studied black mat sediment
samples from 10 archaeological sites dating
back to the Clovis people, the first human
inhabitants of the New World. Researchers
conducted geochemical analysis of the samples
to determine their makeup and also ran carbon
dating tests to determine the age of the samples.
Directly beneath the black mat, researchers
found high concentrations of magnetic grains
containing iridium, charcoal, soot, carbon
spherules, glass-like carbon containing
nanodiamonds and fullerenes packed with
extraterrestrial helium --- all of which
are evidence for an extraterrestrial impact
and the raging wildfires that might have
followed.
Schultz, professor of geological sciences at
Brown and an impact specialist, said the most
provocative evidence for an extraterrestrial
impact was the discovery of nanodiamonds,
microscopic bits of diamond formed only
from the kind of intense pressure you'd
get from a comet or meteorite slamming
into the Earth.
We don't have a smoking gun for our
theory, but we sure have a lot of shell
casings, Schultz said. Taken together,
the markers found in the samples offer
intriguing evidence that North America
had a major impact event about 12,900
years ago.
Schultz admits that there is little decisive
evidence about the actual details about the
impact and its effects. Scientists suspect
that a carbon-rich asteroid or comets were
the culprits. The objects would have exploded
over North America or slammed into it, or both,
shattering and melting ice sheets, sparking
extreme wildfires, and fueling hurricane-force
winds -- all of which could have contributed
to changes in climate that led to the cooling
of the Younger Dryas period.
Our theory isn't a slam dunk, Schultz said.
We need to study a lot more sediments to get
a lot more evidence. But what is sobering about
this theory of ours is that this impact would
be so recent. Not so long ago, something may
have fallen from the sky and profoundly changed
our climate and our culture.
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