Clovis Comet Debate - The Archaeological Conservancy

soil from seven well-dated Clovis sites. “It was one of the
most difficult, labor intensive tasks I’ve ever undertaken,” he
says. “I had to extract the magnetic particles, sprinkle them
on a slide, look at them through a microscope, and count
them. I spent 16 months on the project and over a hundred
hours in the lab. I found no peaks in microspherules at the
start of the Younger Dryas. I could find no support for an
extraterrestrial impact.”
University of Hawaii geologist Francois Paquay couldn’t
either. He checked Clovis-age soil samples for high levels of
iridium, a silvery white metal. Iridium served as a definitive
marker for meteorite impact that marked the end of the age
of dinosaurs, but he found little evidence of the metal in the
samples.
University of Wisconsin-Madison paleoecologist Jacquelyn
Gill examined Clovis-age lake sediments in Indiana and
Ohio for unusual levels of charcoal, magnetic grains, silicate
spheres, titanium, and chromium—all suggested as diagnostic
signatures by Firestone and his team. She reported “no
physical trend to suggest an impact event.”
Andrew Scott, a University of London geologist, did
find something when he examined Clovis-age sediments in
search of carbon spherules the PNAS authors claim is evidence
of an impact, but it wasn’t what they had been hoping
for. He says the organic particles were merely “fecal pellets
from insects, plant or fungal galls, and wood, some of which
may have been exposed to regularly occurring low-intensity
wildfires.”
The comet proponents maintain that the most persuasive
evidence of an extraterrestrial impact is the discovery, at
six Clovis-age sites across North America, of nanodiamonds—
diamonds that are mere billionths of a meter in diameter—
that they say could only be produced in the intense heat and
pressure of the massive impact.
Clovis comet proponents believe an extraterrestrial impact
produced this microscopic diamond found at the
Arlington Springs site in California.
Archaeologist Todd Surovell measured the amount of magnetic
microspherules in soil samples taken from seven Clovis sites.
After placing the samples in water (top), he extracted the microspherules
using an extremely powerful magnet wrapped in a plastic
bag (middle). The microspherules, which adhered to the bag, were
then cleaned in a series of baths (above). He did not find an increase
in microspherules that would corroborate the comet theory.
“The concentrations of nanodiamonds we found at all
six locations exist only in sediments associated with the
Younger Dryas boundary layer, not above it or below it,”
says archaeologist Doug Kennett. “These discoveries provide
strong evidence for a cosmic impact event at approximately
12,900 years ago that would have had enormous environmental
consequences for plants, animals, and humans across
North America.”
But some geologists aren’t so sure. As part of a comprehensive
look at all of the 175 craters caused by extraterrestrial
impacts, Bevan French of the Smithsonian Institution
and Christian Koeberl the University of Vienna also looked
at the Clovis comet claims. They reported that while microscopic
diamonds might, in some cases, be the result of a collision,
they are not proof positive. They concluded that “none
16 fall • 2010
nicole WagUeSpack
allen WeST