Thursday, July 5, 2007

Ancient Humans in Asia Survived Super-Eruption, Find Suggests

Ancient Humans in Asia Survived Super-Eruption, Find Suggests
Anne Casselman
for National Geographic News

July 5, 2007

A group of rocks that could easily be mistaken for gravel suggests that modern humans were in India spearing dinner and filleting meat 76,000 years ago, according to an international team of scientists.

The stone tools were found both above and below a layer of ash left behind by a volcanic "supereruption" 74,000 years ago. The discovery hints that humans in the region survived the blast's devastating effects.

The eruption of Toba, in what is now Indonesia, was the largest volcanic event of the last two million years (see map of Asia).

Toba spewed as much as 720 cubic miles (3,000 cubic kilometers) of magma, rained sulfuric acid down as far away as Greenland, and sent the world into a volcanic winter followed by a severe ice age.

It showered all of India with nearly 6 inches (15 centimeters) of volcanic ash, which acts as a marker of age in Earth's strata today (see a map of the eruption's effects).

Anthropologist Michael Petraglia and his colleagues unearthed stone tool assemblages from above and below the Toba ash deposit in India's Jwalapuram Valley.

"We saw some stone tools above the ash, but we decided to test below the ash," said Petraglia, of the University of Cambridge, England, and primary author of the study.

"It was a lucky strike."

The tools the team found resemble those made by modern humans in Africa, suggesting that the Indian ones could have been made by humans, too, Petraglia said.

"The fact that we have this ash is just icing on the cake, because it tells us that if it's modern humans, then they were able to persist through a major eruptive event," he said. "But they would have had a very, very difficult time."

The study appears in the latest issue of the journal Science.

Volcanic Winter 74,000 years ago

The Toba eruption suspended volcanic gas and sulfuric acid in the stratosphere for years, reflecting warm sunlight away from Earth.

Ice cores reveal that the world was cooler by 5.4 to 9 degrees Fahrenheit (3 to 5 degrees Celsius) for several centuries following the event.

"It would have been more challenging times," said Will Harcourt-Smith, a paleontologist at the American Museum of Natural History in New York who was not involved in the study.

"My point is that humans were complex enough at this point to have dealt with that."

In Africa at this time, humans were exhibiting early symbolism, complex toolmaking behavior, and sophisticated social behavior, he said.

(Read related story: "Is Bead Find Proof Modern Thought Began in Africa?" [March 31, 2004].)

"These people are not behaviorally like you or I, but they are modern humans and they have many of the vestiges of humanity," Harcourt-Smith said.

Humans or Neandertals?

Some experts caution that telling the difference between human-made stone tools and those made by the now extinct Neandertals (or Neanderthals) is tricky business.

"Previous research on this subject has shown that South African and Neanderthal European [stone tool] assemblages are technologically and typologically indistinguishable," said Stanley Ambrose, an archaeologist at the University of Illinois at Urbana-Champaign in Urbana who was not involved in the current study.

"[The study authors] have a bagful of artifacts on which they're drawing conclusions that can only be confirmed by fossil evidence, and they don't have any fossils."

Chris Clarkson, an archaeologist at Australia's University of Queensland and one of the study's authors, said a large piece of ground ochre was found below the ash with the stone tools. Ochre was used by early humans for art, symbols, curing hides, or helping to attach stone tools to build a wooden shaft.

"All of these potential uses hint at more complex behaviors than are usually attributed to earlier extinct hominin species, although we know European Neanderthals also used ochre a lot," Clarkson said.

"More excavation will help us resolve whether this assemblage belongs to modern humans or not."

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