Possibly a Permian-Triassic meteoroid swarm, which gradually diminished
over time.
The fragmentation of just one large earth-crossing asteroid could account
for the temporal clustering of craters on earth during this period. If
the resulting fragments were also earth-crossers, then the earth would
eventually have swept them up within a few million years (maybe a bit
longer).
Also note that the entire Triassic was a time of rather large cosmic
smacks.
214 mya (+/- large error bar): Manicouagan impact
214 mya (+/- large error bar): Rochechouart in central France
Even when the error is taken into account, both craters lay comfortably
with the Late Triassic.
The Manicouagan and Rochechouart impactors may have been the last of the
big pieces to be swept up from the earth crossers that began falling at
the Permian-Triassic boundary. Therefore, it is entirely possible that
impact events separated by tens of millions of years may have had a
common genesis.
Just speculation of course.
<pb>
--
On Fri, 02 Jun 2006 18:25:14 +0100 john hunt <john.bass@ntlworld.com>
writes:
And what about this:
http://www.sciencedaily.com/releases/2004/05/040514025854.htm
250mya craters seem to be turning up all the time! This one is only
a
tiddler though.
-----Original Message-----
From: owner-DINOSAUR@usc.edu [mailto:owner-DINOSAUR@usc.edu] On
Behalf Of
Richard W. Travsky
Sent: 02 June 2006 16:43
To: dinosaur@usc.edu
Subject: Big 250 mya Crater Found In Antarctica
http://www.sciencedaily.com/upi/index.php?feed=Science&article=UPI-1-2006
060
1-18311100-bc-us-giantcrater.xml
COLUMBUS, Ohio, June 1 (UPI) -- U.S. planetary scientists report
finding
evidence of a meteor impact much larger than the one believed
responsible
for the extinction of dinosaurs.
The 300-mile-wide crater lies more than a mile beneath the East
Antarctic
Ice Sheet and might date to about 250 million years ago -- the time
of the
Permian-Triassic extinction, when nearly all animal life on Earth
became
extinct.
Its size and location -- in the Wilkes Land region of East
Antarctica,
south of Australia -- suggest it could have begun the breakup of the
Gondwana supercontinent by creating the tectonic rift that pushed
Australia northward.
Scientists believe the Permian-Triassic extinction paved the way for
dinosaurs to rise to prominence. The Wilkes Land crater is more than
five
times the size of the Chicxulub crater in the Yucatan peninsula,
which
marks the impact that may have ultimately killed the dinosaurs 65
million
years ago.
Ohio State University researchers who made the discovery
collaborated with
the National Aeornautics and Space Administration, Russian and South
Korean scientists in the study.
The preliminary results of their research were presented during a
recent
poster session at the American Geophysical Union Joint Assembly
meeting in
Baltimore.
--
Former White House hunter safety instructor.
Current liaison between the U.S. military and the Iraqi citizens.
Please, someone just shoot me.
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