Imprensa: "First Americans arrived 2500 years before we thought"

Sat Mar 26 14:18:23 UTC 2011

Matéria da revista New Scientist (24/mar/2011)
http://www.newscientist.com/article/dn20287-first-americans-arrived-2500-years-before-we-thought.html

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First Americans arrived 2500 years before we thought

(24 March 2011 by Ferris Jabr)

It's time to rewrite the story of how Stone Age explorers from Asia
crossed over into the Americas and colonised the continents.

The Clovis people were leading candidates for the title of first
Americans. But a hoard of tools newly uncovered in Texas suggests the
land was inhabited several thousand years before the reign of the
Clovis culture.

When the people who built the Texan tools migrated, ice sheets would
have made travel by land difficult. This lends strength to the
hypothesis that the Americas were colonised by sea, not land.

Who the first Americans were, where they came from and when they
arrived are contested issues among archaeologists. One favoured
theory, known as "Clovis first", says that during the last Ice Age,
people from Asia followed herd animals across a land bridge connecting
Siberia to Alaska and established the first settlements in North
America. The Clovis culture is characterised by pointed stone tools.

But recent finds of artefacts that pre-date the Clovis, including this
new one in Texas, have challenged the Clovis-first hypothesis.
Flakes and stones

The new hoard contains 15,528 items, the largest group of pre-Clovis
stone objects ever found. It includes 56 well-preserved tools amongst
many stone chips, flakes and fragments that probably broke off other
tools.

"What we have found is evidence of early human occupation dating back
to 15,500 years ago, 2500 years older than Clovis," says Michael
Waters of Texas A&M University in College Station, lead author of the
study.

Waters and his team discovered the primitive toolkit in a
well-preserved layer of soil at Buttermilk Creek in central Texas.
Directly above it lay another, distinct layer dating from the Clovis
era.

The objects are clearly shaped by human hands, but less sophisticated
than Clovis tools – the team describe them as prototypes. The hallmark
of Clovis technology is a carefully chiselled, oval-shaped stone with
thin razor-sharp edges and a notch in the bottom for hafting to a
spear or knife handle. In contrast, the newly discovered tools are not
well-shaped, lack notches and are lighter than Clovis tools. Waters
thinks that descendants of their makers may have later invented Clovis
technology.
Difficult dating

Establishing that the objects were indeed older than the Clovis proved
a challenge. The team did not find enough organic matter at the site
to pinpoint the age of the tools with radiocarbon dating. Instead they
relied on a newer and slightly less accurate technique called
optically stimulated luminescence, which uses light to free electrons
trapped in minerals.

Others agree the find is significant. "This looks to me like a really
solid example of archaeology that is older than dates people associate
with Clovis," says Douglas Bamforth of the University of Colorado at
Boulder. "They have done a great job of documenting the age of the
sediment."

Dennis Jenkins of the University of Oregon in Eugene is similarly
impressed, but points out that the tools could have shifted through
the ages. "Nobody will argue these artefacts aren't real, but the
question is whether they were really found exactly where they belonged
or whether they settled from above."
Quiet grave

Burrowing rodents, plant roots and geologic activity all create cracks
and voids in soil. The artefacts could have slipped over time through
such gaps from the higher Clovis layer to the older Buttermilk Creek
layer. But Waters and his team argue this is not likely to have
happened here.

Firstly, the site is not especially geologically active and the team
did not find any cracks large enough for objects to sift through.
Secondly, if the earth had shifted, allowing the artefacts to move
about, the changes would show in the magnetic signatures of different
layers of soil; the team analysed the magnetic record, but found no
such signs of disturbance.

Finally, the team showed that they could piece stone flakes together
like pieces of a 3D jigsaw puzzle, and the pieces that fitted together
always came from a single layer of earth. In other words, the
fragments had not moved from their original burial site.
Paradigm shift

The new finds also suggest that the bridge between Asia and America
was not the only route into the Americas. Fifteen thousand years ago,
people in Siberia could not easily have crossed to Alaska and down
into North America because the major ice sheets at the time were
fused, prohibiting travel through North America after crossing the
bridge. Instead, whoever made the stone tools at the Buttermilk Creek
site may have journeyed to the New World by sea.

"I think we are on the edge of a paradigm shift now," says Waters.
"We're past the Clovis-first model. We have robust evidence of people
here before Clovis that is in a secure geological context and
well-dated. Now we can seriously sit down and develop a new model for
the peopling of the Americas."

Bamforth echoed his opinions. "It might be time to stop talking about
Clovis-first altogether."

Journal reference: Science, DOI: 10.1126/science.1201855

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