Oldest North American Rock Art May Be 14,800 Years Old
Nevada petroglyphs could date back to the first peopling of the Americas.
Petroglyph-inscribed rocks.
Photograph courtesy Larry Benson, University of Colorado
Published August 15, 2013
Ancient symbols etched onto the sides of boulders lying along
the western edge of a desiccated lake in Nevada are the oldest
confirmed rock carvings in North America—possibly dating back to the
first peopling of the New World, scientists say.
The carbonate ages, combined with an analysis of sediment cores taken
from neighboring Pyramid Lake, suggest that the boulders were exposed
to air—and thus accessible for carving by humans—between about 14,800 to
13,100 years ago, and again from about 11,300 to 10,500 years ago. In
between the two time periods, the boulders were submerged, the
scientists say.
"At the moment we have no way to decide between the two possibilities."
The so-called petroglyphs, carved in soft limestone
millennia ago, range from simple lines, pits, and swirls to more complex
and ambiguous shapes that resemble diamonds, trees, flowers, and veins
in a leaf. They range from about 8 inches (20 centimeters) up to about 3
feet (1 meter) in width.
In a new study, published in this month's issue of the Journal of Archaeological Science, geochemist Larry Benson
and his team concluded that the petroglyphs, located about 35 miles (56
kilometers) northeast of Reno at Winnemucca Lake, are at least 10,500
years old, and perhaps as much as 14,800 years old.
"Whether they turn out to be as old as 14,800 years ago or
as recent as 10,500 years ago, they are still the oldest petroglyphs
that have been dated in North America," Benson, who is at the University
of Colorado Natural History Museum in Boulder, said in a statement.
(See video of rock art in Arizona.)
Clues in Carbonate
To date the petroglyphs, Benson and his colleagues began by figuring out just when they could have been made.
Though Winnemucca Lake is dried up now, it was once so full
of water that the boulders upon which the petroglyphs are etched were
submerged.
As the water levels slowly dropped, crusts of a mineral
called carbonate formed on the boulders. Radiocarbon testing of these
carbonate layers revealed them to range in age from about 14,800 to
10,300 years old.
It's unknown what method was used to create the
petroglyphs, but one possibility is the artists used hard volcanic rock
to chip away at the carbonate, which is porous and relatively soft, said
Benson, who conducted the dating research while with the U.S.
Geological Survey.
As a result, the rock art would not have taken very long to
carve, but "whether all of them were done within a short period of time
or over a span of hundreds of years, I don't know," Benson said in an
interview on Wednesday.
Rocks with petroglyphs of trees and diamonds.
Photograph courtesy Larry Benson, University of Colorado
Non-invasive Examination
Benson said it might be possible to better pinpoint the age
of the petroglyphs, but it would require sampling carbonate from inside
the etchings themselves—something that he has agreed not to do.
Benson obtained permission to non-invasively examine the carvings from the Pyramid Lake Paiute Tribe, which owns the land.
"One of the deals I made was that I would only work to the
side of the glyphs, and not touch any of the glyphs themselves," Benson
said.
Mystery Artists
Prior to the new dating of the Lake Winnemucca petroglyphs,
the oldest rock art in North America was thought to be carvings found
at Long Lake in Oregon that date to roughly 7,300 years ago.
Benson says he doesn't know what the symbols at Lake
Winnemucca mean, or who might have made them, but he notes that their
ages roughly match those of several pieces of fossilized human feces, or
coprolites, that were discovered in Paisley Cave in Oregon and dated to
around 14,400 to 13,000 years ago.
This date is close to when scientists think humans first
began settling the Americas. In a new study published in this week's
issue of the journal of the Proceedings of the National Academy of Sciences,
scientists say they have found genetic evidence that a first wave of
migrants crossed into the Americas from Asia about 15,000 to 18,000
years ago by slowly creeping down the continent's coasts.
A few thousand years later, according to the study, a
second wave of humans entered North America, this time by slipping
across the Bering Strait into Alaska and then crossing through an
ice-free corridor into Canada.
Benson speculated that members of the first wave of settlers might have been responsible for the Lake Winnemucca rock art.
"It's possible that those people did occupy areas farther
south, like the Lake Winnemucca area ... [but] it is also possible that
paleoindians occupying the Winnemucca Lake basin between 11,300 and
10,500 years ago carved the petroglyphs," he said.
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