40,000 BC footprints in Mexico debunked
- From: Topiltzin-2091@xxxxxxxxx
- Date: Thu, 1 Dec 2005 08:50:44 -0600
Public release date: 30-Nov-2005
Contact: Robert Sanders
rsanders@xxxxxxxxxxxx
510-643-6998
University of California - Berkeley
Alleged 40,000-year-old human footprints in Mexico much, much older than
thought
Berkeley -- Alleged footprints of early Americans found in volcanic rock
in Mexico are either extremely old - more than 1 million years older
than other evidence of human presence in the Western Hemisphere - or not
footprints at all, according to a new analysis published this week in
Nature.
The study was conducted by geologists at the Berkeley Geochronology
Center and the University of California, Berkeley, as part of an
investigative team of geologists and anthropologists from the United
States and Mexico.
Earlier this year, researchers in England touted these "footprints" as
definitive proof that humans were in the Americas much earlier than
11,000 years ago, which is the accepted date for the arrival of humans
across a northern land-bridge from Asia.
These scientists, led by geologist Silvia Gonzalez of Liverpool's John
Moores University, dated the volcanic rock at 40,000 years old. They
hypothesized that early hunters walked across ash freshly deposited near
a lake by volcanoes that are still active in the area around Puebla,
Mexico. The so-called footprints, subsequently covered by more ash and
inundated by lake waters, eventually turned to rock.
But Paul Renne, director of the Berkeley Geochronology Center and an
adjunct professor of earth and planetary science at UC Berkeley, and his
colleagues in Mexico and at Texas A&M University report in the Dec. 1
issue of Nature a new age for the rock: about 1.3 million years.
"You're really only left with two possibilities," Renne said. "One is
that they are really old hominids - shockingly old - or they're not
footprints."
Renne's colleagues are Michael R. Waters, director of the Center for the
Study of the First Americans at Texas A&M University; Joaquin
Arroyo-Cabrales and Mario Perez-Campa of the Mexican National Institute
of Anthropology and History; Patricia Ochoa Castillo of the Mexican
National Museum of Anthropology; and UC Berkeley graduate students
Joshua M. Feinberg and Kim B. Knight. The Berkeley Geochronology Center,
located a block from the UC Berkeley campus, is one of the world's
preeminent anthropological dating laboratories.
Paleoanthropologist Tim White, professor of integrative biology at UC
Berkeley, is familiar with the "so-called footprints" and knows Renne
well, frequently collaborating with him in the dating of
million-year-old sediments in an area of Ethiopia where White has
excavated numerous fossils of human ancestors. He is not surprised at
the new finding.
"The evidence (the British team) has provided in their arguments that
these are footprints is not sufficient to convince me they are
footprints," said White, who did not contribute to the new work that
Renne's group is reporting in Nature. "The evidence Paul has produced by
dating basically means that this argument is over, unless indisputable
footprints can be found sealed within the ash."
Renne determined the new date using the argon/argon dating technique,
which reliably dates rock as young as 2,000 years or as old as 4 billion
years. The British-led researchers, however, relied mainly on carbon-14
dates of overlying sediments. Carbon-14 cannot reliably date materials
older than about 50,000 years.
The idea for another test that, it turns out, throws more cold water on
the footprint hypothesis came to Renne one morning in the shower. Many
rocks retain evidence of their orientation at the moment they cool in
the form of iron oxide grains magnetized in a direction parallel to the
Earth's magnetic field at the time of cooling. Because the Earth's field
has repeatedly flipped throughout the planet's history, it is possible
to date rock based on its magnetic polarity.
Feinberg found that the rock grains in the volcanic ash had polarity
opposite to the Earth's polarity today. Since the last magnetic pole
reversal was 790,000 years ago, the rock must be at least that age.
Because the Earth's magnetic polarity changes, on average, every 250,000
years, the argon/argon date is consistent with a time between 1.07 and
1.77 million years ago when the Earth's polarity was opposite to that of
today.
Moreover, Feinberg found that each individual grain in the rock is
magnetized in the same direction, meaning that the rock has not been
broken up and reformed since it was deposited. This makes extremely
unlikely the possibility that the original ash had been weathered into
sand that early humans walked through before the sand was welded into
rock again.
"Imagine two-millimeter-wide BBs cemented together where they're
touching," Feinberg said. "The paleomagnetic data tell us that these
things did not move around at all since they were deposited. They
haven't been eroded and redeposited anywhere else. They fell while they
were still hot, which raises the question of the validity of the
footprints. If they were hot, why would anybody be walking on them?"
The British researchers, funded by the United Kingdom's Natural
Environment Research Council, have promoted their hypothesis widely,
most prominently at a July 4, 2005, presentation and press conference at
the Royal Society's Summer Science Exhibition 2005 in London. The team,
which includes Gonzalez as well as Professor David Huddart from John
Moores University, also involves scientists from Bournemouth University,
the University of Oxford and the Australian National University. They
have yet to publish a peer-reviewed analysis of the footprints.
In all, the British team claims to have found 250 footprints - mostly
human, but also dog, cat and cloven-hoofed animal prints - in a layer of
volcanic ash deposited in a former lake bed now exposed near a reservoir
outside Puebla. Its dating techniques returned a date of 40,000 years
ago, in contrast to the oldest accepted human fossil from the Americas,
an 11,500-year-old skull. This makes the rock "one of the most important
areas in the study of early human occupation in the Americas and would
support a much earlier human migration than is currently accepted," the
team wrote.
One of the team members, Matthew Bennett of Bournemouth, was quoted on a
Royal Society Web site as saying, "Accounting for the origin of these
footprints would require a complete rethink on the timing, route and
origin of the first colonization of the Americas."
Renne, Knight, Waters and the Mexico City archeologists visited the site
at the Toluquilla quarry last year while collecting rocks from another
anthropological site across the reservoir. Renne noted that the black,
basaltic rock is very tough and is mined in slabs for building.
Pre-Columbian Mexicans also constructed buildings from the rock, which
they called xalnene, meaning "fine sand" in the Nahuatl language. Today,
trucks headed toward the quarry routinely drive across the xalnene tuff
in which the alleged footprints are found, and the rock itself is
pockmarked with many depressions in addition to the alleged footprints.
"They're scattered all over, with no more than two or three in a
straight line," which would be expected if someone had walked through
the ash, Renne said. If the depressions were footprints, they could not
have been made by modern humans, he noted, since even in Africa, Homo
sapiens did not appear until about 160,000 years ago. Given the age of
the volcanic rock and lacking other evidence of early human ancestors in
the Americas 1.3 million years ago, the researchers wrote in their
paper, "we consider such a possibility to be extremely remote."
Many paleontologists have withheld judgment on the alleged footprints,
awaiting good geological dates, Feinberg said. "With this study, we're
trying to nip any misrepresentation in the bud."
###
The research was supported by the Center for the Study of the First
Americans, the North Star Archaeological Research Program and the
Berkeley Geochronology Center.
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