[meteorite-list] Giant Meteorite Impact 65 Millions Years Ago May Not Have Set The World On Fire

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:17:38 2004
Message-ID: <200312032033.MAA12372_at_zagami.jpl.nasa.gov>

http://www.nature.com/nsu/031201/031201-3.html

Giant meteorite impact 65 million years ago may not have set the
world on fire.

PHILIP BALL
Nature Science Update
03 December 2003

New evidence questions the idea that a meteorite impact
thought to have wiped out the dinosaurs triggered worldwide
wildfires.

A crater about 180 kilometers wide attests to an asteroid
having hit Earth at Chicxulub on the Yucatan Peninsula in
Mexico 65 million years ago. But even about 2,000 km from
here there were no big fires, claim Claire Belcher of Royal
Holloway College in London, UK and her colleagues[1]. So there
can't have been global conflagrations, conclude the researchers.

The group found no charcoal in sedimentary rocks laid down at the
time - the end of the Cretaceous period when 85 per cent of
all species seem to have become extinct. Other geologists have
argued that soot in similar rocks elsewhere is a sign that the
meteorite released enough heat to spark fires everywhere.

Traces of the impact have been found in sediments around the world.
Rocks from the Cretaceous-Tertiary or K-T boundary contain
a sprinkling of the element iridium, believed to have been carried by
the meteorite. They are also peppered with tiny glass-like blobs, the
frozen remains of molten rock flung high into the air at the impact site.

Some have proposed that this hot debris would have ignited
vegetation wherever it fell to earth. Others believe a gigantic fireball,
rising over Chicxulub, would have spread hot material over the
planet. Either way, widespread wildfires would have helped wipe out
life on land.

Charcoal could have been produced only from burnt vegetation, says
Belcher's team. So they looked for it in K-T sedimentary
rocks across North America, from Colorado in the south to
Saskatchewan in the north.

Soot, the researchers argue, could have come from other sources. The
particles could have been blown in from afar or produced from oil, coal
and gas burnt up at the impact site.

Another possible cause of the mass extinctions is the dust thrown
into the atmosphere by the meteorite - it might have blocked
out the Sun's heat and light. In other words, the dinosaurs might
have frozen, not roasted.

References

   1. Belcher, C.M., Collinson, M.E., Sweet, A.R., Hildebrand,
      A.R. & Scott, A.C. Fireball passes and nothing burns-The
      role of thermal radiation in the Cretaceous-Tertiary event:
      Evidence from the charcoal record of North America. Geology,
      31, 1061 - 1064, (2003). |Article|
Received on Wed 03 Dec 2003 03:33:17 PM PST