PureInsight | October 21, 2007
What caused the extinction of mammoths and the decline of Stone Age
people about 13,000 years ago remains hotly debated. Overhunting by
Paleoindians, climate change and disease lead the list of probable
causes. But an idea once considered a little out there is now hitting
closer to home.
A team of international researchers, including two Northern Arizona
University geologists, reports evidence that a comet or low-density
object barreling toward Earth exploded in the upper atmosphere and
triggered a devastating swath of destruction that wiped out most of the
large animals, their habitat and humans of that period.
"The detonation either fried them or compressed them because of the
shock wave," said Ted Bunch, NAU adjunct professor of geology and
former NASA researcher who specializes in impact craters. "It was a
mini nuclear winter."
Bunch and Jim Wittke, a geologic materials analyst at NAU, are
co-authors of the paper, which fingers an extraterrestrial impact
12,900 years ago for the mass extinctions at the end of the Ice Age.
The paper was just released online in the Proceedings of the National
Academy of Sciences. The research team includes several members of the
U.S. National Academy of Sciences and researchers from Hungary and the
Netherlands.
No one has found a giant crater in the Earth that could attest to such
a cataclysmic impact 13,000 years ago, but the research team offers
evidence of a comet, two and a half to three miles in diameter, that
detonated 30 to 60 miles above the earth, triggering a massive
shockwave, firestorms and a subsequent drastic cooling effect across
most of North America and northern Europe.
"The comet may have broken up into smaller pieces as it neared the
Earth and then these pieces detonated in various places above two
continents," Bunch said.
The evidence for multiple detonations comes from a four-inch-thick
"black mat" of carbon-rich material that appears as far north as
Canada, Greenland and Europe to as far south as the Channel Islands off
the coast of California and eastward to the Carolinas. Two sites exist
in Arizona at Murray Springs and Lehner Ranch, both near Sierra Vista.
Evidence of mammoths and other megafauna and early human hunters, known
as the Clovis culture, are found beneath the black mat but are missing
entirely within or above it. This led the research team to conclude an
extraterrestrial impact wiped out many of the inhabitants of the Late
Pleistocene. Bunch notes that some animals may have survived in
protected niches.
The black mat was formed by ponding of water and algal blooms and
contains carbon, soot and glassy carbon - remnants of burned materials.
Some of these remnants are extraterrestrial in nature. For example, the
research team has identified fullerenes, spherical carbon cages
resembling a soccer ball, which are formed in shock events outside the
Earth's atmosphere. Trapped inside the fullerenes is a concentration of
helium 3 that is many times greater than what is found in the Earth's
atmosphere.
A colorized
scanning electron microscope image of a glassy carbon sphere that
contains evidence of extraterrestrial impact. The sphere measures about
.012 inches in width. [Credit: SEM imaging by Jim Wittke]
The black mat also has turned up nanodiamonds, which are formed in the
interstellar medium outside the solar system, by or by a high-explosive
detonation.
"Either these things came in with the impactor or they were made during
impact detonation. We have no other explanation for their presence,"
Bunch said.
The magnitude of the detonations would have been huge.
"A hydrogen bomb is the equivalent of about 100 to 1,000 megatons,"
Bunch said. "The detonations we're talking about would be about 10
million megatons. That's larger than the simultaneous detonation of all
the world's nuclear bombs past and present."
The research team believes the detonations destabilized a vast ice
sheet, known as the Laurentide Ice Sheet, that covered most of what was
then Canada and the northern United States. Heat from the detonation
and firestorms would have melted much of the ice sheet, releasing water
vapor into the atmosphere.
"The result was rapid cooling of about eight degrees over the next 100
years," Bunch said. The melting of the ice sheet and subsequent climate
change would explain the water-based nature of the black mat.
Catastrophic extraterrestrial impacts are not new. Scientists theorize
a much larger asteroid impact annihilated the dinosaurs and about 85
percent of the Earth's biomass about 65 million years ago. The most
recent incident, known as the Tunguska event, occurred in 1908 in
Russia. The Tunguska explosion was an airburst of a comet or meteorite
estimated at 10-15-megatons that destroyed tens of millions of trees
across more than 800 square miles.
Bunch says impact airbursts may be more common than previously thought
with possibly two or three such events having occurred over the last
100,000 years. And more are sure to follow.
[Editors' note: Their count is a little off. As it says in "The First Talk" of Zhuan Falun,
"The movement of our planet earth, when it's in this vast universe, and
when it's in this turning Milky Way, there's just no way it could have
always had smooth sailing, and chances are it's run into other planets,
or had other problems, and these would have brought about huge
catastrophes. If we look at it from the perspective of abilities,
that's just how it was arranged. One time I traced it back carefully
and found out that there have been 81 times when mankind lay in total
ruin, and only a few people survived, only a little of the prehistoric
civilization was left, and then they entered the next period and lived
primitively. When the people multiplied enough, civilization would
finally appear again. So it's gone through 81 of these cycles, and I
didn't trace it back to the end."]
