[meteorite-list] Ice Age Blast 'Ravaged America' 13,000 Years Ago

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon, 21 May 2007 11:08:29 -0700 (PDT)
Message-ID: <200705211808.LAA28461_at_zagami.jpl.nasa.gov>

http://news.bbc.co.uk/2/hi/science/nature/6676461.stm

Ice Age blast 'ravaged America'
BBC News
May 21, 2007

A controversial new idea suggests that a large space rock exploded over
North America 13,000 years ago.

The blast may have wiped out one of America's first Stone Age cultures
as well as the continent's big mammals such as the mammoth and the
mastodon.

The blast, from a comet or asteroid, caused a major bout of climatic
cooling which may also have affected human cultures emerging in Europe
and Asia.

Scientists will outline their evidence this week at a meeting in Mexico.

The evidence comes from layers of sediment at more than 20 sites across
North America.

These sediments contain exotic materials: tiny spheres of glass and
carbon, ultra-small specks of diamond - called nanodiamond - and amounts
of the rare element iridium that are too high to have come from Earth.

All, they argue, point to the explosion 12,900 years ago of an
extraterrestrial object up to 5km across.

No crater remains, possibly because the Laurentide Ice Sheet, which
blanketed thousands of sq km of North America during the last Ice Age,
was thick enough to mask the impact.

Another possibility is that it exploded in the air.

Climate cooling

The rocks studied by the researchers have a black layer which, they
argue, is the charcoal deposited by wildfires which swept the continent
after the explosion.

Clovis hunting points, Center for the Study of the First Americans
The Clovis people developed an advanced stone tool technology

The blast would not only have generated enormous amounts of heat that
could have given rise to wildfires, but also brought about a period of
climate cooling that lasted 1,000 years - an event known as the Younger
Dryas.

Professor James Kennett, from the University of California in Santa
Barbara (UCSB), said the explosion could be to blame for the extinction
of several large North American mammals at the end of the last Ice Age.

"All the elephants, including the mastodon and the mammoth, all the
ground sloths, including the giant ground sloth - which, when standing
on its hind legs, would have been as big as a mammoth," he told the BBC.

"All the horses went out, all the North American camels went out. There
were large carnivores like the sabre-toothed cat and an enormous bear
called the short-faced bear."

Professor Kennett said this could have had an enormous impact on human
populations.

Population decline

According to the traditional view, humans crossed from north-east Asia
to America at the end of the last Ice Age, across a land bridge which -
at the time - connected Siberia to Alaska.

The Clovis culture was one of the earliest known cultures in the
continent. These proficient hunter-gatherers developed a distinctive
thin, fluted spear head known as the Clovis point, which is regarded as
one of the most sophisticated stone tools ever developed.

Archaeologists have found evidence from the Topper site in South
Carolina, US, that Clovis populations here went through a population
collapse.

But there is no evidence of a similar decline in other parts of the
continent. The Clovis culture does vanish from the archaeological record
abruptly, but it is replaced by a myriad of different local
hunter-gatherer cultures.

Jeff Severinghaus, a palaeoclimatologist at Scripps Institution of
Oceanography in California, told Nature magazine: "Their impact theory
shouldn't be dismissed; it deserves further investigation."

According to the new idea, the comet would have caused widespread
melting of the North American ice sheet. The waters would have poured
into the Atlantic, disrupting its currents.

This, they say, could have caused the 1,000 year-long Younger Dryas cold
spell, which also affected Asia and Europe.

The Younger Dryas has been linked by some researchers to changes in the
living patterns of people living in the Middle East which led to the
beginning of farming.

A massive explosion near the Tunguska river, Siberia, in 1908, is also
thought to have been caused by a space rock exploding in the atmosphere.
It felled 80 million trees over an area of 2,000 sq km.

The new theory will be presented and debated at the American Geophysical
Union's Joint Meeting in Acapulco, Mexico, this week.
Received on Mon 21 May 2007 02:08:29 PM PDT