[meteorite-list] Comet May Have Exploded Over North America 13, 000 Years Ago

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 16 Aug 2007 14:25:28 -0700 (PDT)
Message-ID: <200708162125.OAA00072_at_zagami.jpl.nasa.gov>

http://www.nsf.gov/discoveries/disc_summ.jsp?cntn_id=109768&org=NSF

Comet May Have Exploded Over North America 13,000 Years Ago

Caused wooly mammoth extinction, global cooling and end of early human
Clovis culture

National Science Foundation
August 14, 2007

New scientific findings suggest that a large comet may have exploded
over North America 12,900 years ago, explaining riddles that scientists
have wrestled with for decades, including an abrupt cooling of much of
the planet and the extinction of large mammals.

The discovery was made by scientists from the University of California
at Santa Barbara and their colleagues. James Kennett, a
paleoceanographer at the university, said that the discovery may explain
some of the highly debated geologic controversies of recent decades.

The period in question is called the Younger Dryas, an interval of
abrupt cooling that lasted for about 1,000 years and occurred at the
beginning of an inter-glacial warm period. Evidence for the temperature
change is recorded in marine sediments and ice cores.

According to the scientists, the comet before fragmentation must have
been about four kilometers across, and either exploded in the atmosphere
or had fragments hit the Laurentide ice sheet in northeastern North America.

Wildfires across the continent would have resulted from the fiery
impact, killing off vegetation that was the food supply of many of
larger mammals like the woolly mammoths, causing them to go extinct.

Since the Clovis people of North America hunted the mammoths as a major
source of their food, they too would have been affected by the impact.
Their culture eventually died out.

The scientific team visited more than a dozen archaeological sites in
North America, where they found high concentrations of iridium, an
element that is rare on Earth and is almost exclusively associated with
extraterrestrial objects such as comets and meteorites.

They also found metallic microspherules in the comet fragments; these
microspherules contained nano-diamonds. The comet also carried carbon
molecules called fullerenes (buckyballs), with gases trapped inside that
indicated an extraterrestrial origin.

The team concluded that the impact of the comet likely destabilized a
large portion of the Laurentide ice sheet, causing a high volume of
freshwater to flow into the north Atlantic and Arctic Oceans.

"This, in turn, would have caused a major disruption of the ocean's
circulation, leading to a cooler atmosphere and the glaciation of the
Younger Dryas period," said Kennett. "We found evidence of the impact as
far west as the Santa Barbara Channel Islands."

The National Science Foundation's Paleoclimate Program funded the research.

-- Cheryl Dybas, NSF (703) 292-7734 cdybas at nsf.gov
Received on Thu 16 Aug 2007 05:25:28 PM PDT