http://newswire.ascribe.org/cgi-bin/behold.pl?ascribeid=20050923.103123&time=11%2050%20PDT&year=2005&public=0
Fri Sep 23 11:50:07 2005 Pacific Time
Supernova Explosion May Have Caused Mammoth Extinction
BERKELEY, Calif., Sept. 23 (AScribe Newswire) -- A distant supernova
that exploded 41,000
years ago may have led to the extinction of the mammoth, according to research
that will be
presented tomorrow (Sept. 24) by nuclear scientist Richard Firestone of the
U.S. Department of
Energy's Lawrence Berkeley National Laboratory (Berkeley Lab).
Firestone, who conducted this research with Arizona geologist Allen
West, will unveil this
theory at the 2nd International Conference "The World of Elephants" in Hot
Springs, S.D. Their
theory joins the list of possible culprits responsible for the demise of
mammoths, which last roamed
North America roughly 13,000 years ago. Scientists have long eyed climate
change, disease, or
intensive hunting by humans as likely suspects.
Now, a supernova may join the lineup. Firestone and West believe that
debris from a supernova
explosion coalesced into low-density, comet-like objects that wreaked havoc on
the solar system long
ago. One such comet may have hit North America 13,000 years ago, unleashing a
cataclysmic event that
killed off the vast majority of mammoths and many other large North American
mammals. They found
evidence of this impact layer at several archaeological sites throughout North
America where Clovis
hunting artifacts and human-butchered mammoths have been unearthed. It has long
been established
that human activity ceased at these sites about 13,000 years ago, which is
roughly the same time
that mammoths disappeared.
They also found evidence of the supernova explosion's initial shockwave:
34,000-year-old
mammoth tusks that are peppered with tiny impact craters apparently produced by
iron-rich grains
traveling at an estimated 10,000 kilometers per second. These grains may have
been emitted from a
supernova that exploded roughly 7,000 years earlier and about 250 light years
from Earth.
"Our research indicates that a 10-kilometer-wide comet, which may have
been composed from the
remnants of a supernova explosion, could have hit North America 13,000 years
ago," says Firestone.
"This event was preceded by an intense blast of iron-rich grains that impacted
the planet roughly
34,000 years ago."
In support of the comet impact, Firestone and West found magnetic metal
spherules in the
sediment of nine 13,000-year-old Clovis sites in Michigan, Canada, Arizona, New
Mexico and the
Carolinas. Low-density carbon spherules, charcoal, and excess radioactivity
were also found at these
sites.
"Armed with only a magnet and a Geiger counter, we found the magnetic
particles in the
well-dated Clovis layer all over North America where no one had looked before,"
says Firestone.
Analysis of the magnetic particles by Prompt Gamma Activation Analysis
at the Budapest
Reactor and by Neutron Activation Analysis at Canada's Becquerel Laboratories
revealed that they are
rich in titanium, iron, manganese, vanadium, rare earth elements, thorium, and
uranium. This
composition is very similar to lunar igneous rocks, called KREEP, which were
discovered on the moon
by the Apollo astronauts, and have also been found in lunar meteorites that
fell to Earth in the
Middle East an estimated 10,000 years ago.
"This suggests that the Earth, moon, and the entire solar system were
bombarded by similar
materials, which we believe were the remnants of the supernova explosion 41,000
years ago," says
Firestone.
In addition, Berkeley Lab's Al Smith used the Lab's Low-Background
Counting Facility to
detect the radioactive isotope potassium-40 in several Clovis arrowhead
fragments. Researchers at
Becquerel Laboratories also found that some Clovis layer sediment samples are
significantly enriched
with this isotope.
"The potassium-40 in the Clovis layer is much more abundant than
potassium-40 in the solar
system. This isotope is formed in considerable excess in an exploding
supernova, and has mostly
decayed since the Earth was formed," says Firestone. "We therefore believe that
whatever hit the
Earth 13,000 years ago originated from a recently exploded supernova."
Firestone and West also uncovered evidence of an even earlier event that
blasted parts of the
Earth with iron-rich grains. Three mammoth tusks found in Alaska and Siberia,
which were
carbon-dated to be about 34,000 years old, are pitted with slightly
radioactive, iron-rich impact
sites caused by high-velocity grains. Because tusks are composed of dentine,
which is a very hard
material, these craters aren't easily formed. In fact, tests with shotgun
pellets traveling 1,000
kilometers per hour produced no penetration in the tusks. Much higher energies
are needed: x-ray
analysis determined that the impact depths are consistent with grains traveling
at speeds
approaching 10,000 kilometers per second.
"This speed is the known rate of expansion of young supernova remnants,"
says Firestone.
The supernova's one-two punch to the Earth is further corroborated by
radiocarbon
measurements. The timeline of physical evidence discovered at Clovis sites and
in the mammoth tusks
mirrors radiocarbon peaks found in Icelandic marine sediment samples that are
41,000, 34,000, and
13,000 years old. Firestone contends that these peaks, which represent
radiocarbon spikes that are
150 percent, 175 percent, and 40 percent above modern levels, respectively, can
only be caused by a
cosmic ray-producing event such as a supernova.
"The 150 percent increase of radiocarbon found in 41,000-year-old marine
sediment is
consistent with a supernova exploding 250 light years away, when compared to
observations of a
radiocarbon increase in tree rings from the time of the nearby historical
supernova SN 1006," says
Firestone.
Firestone adds that it would take 7,000 years for the supernova's
iron-rich grains to travel
250 light years to the Earth, which corresponds to the time of the next marine
sediment radiocarbon
spike and the dating of the 34,000-year-old mammoth tusks. The most recent
sediment spike
corresponds with the end of the Clovis era and the comet-like bombardment.
"It's surprising that it works out so well," says Firestone.
- - - -
CONTACT: Dan Krotz, Berkeley Lab Communications, 510-486-4019, [EMAIL
PROTECTED]
ABOUT THE LAB: Berkeley Lab is a U.S. Department of Energy national
laboratory located in
Berkeley, California. It conducts unclassified scientific research and is
managed by the University
of California. Visit our website at http://www.lbl.gov .
Media Contact: Dan Krotz, 510-486-4019, [EMAIL PROTECTED]
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