December 6, 2009

Ancient Volcanic Blast Illuminates History Of Early Humans

Researchers say that a recent study has yielded "incontrovertible evidence" that a massive volcanic eruption on the Indonesian island of Sumatra some 73,000 years ago wrought massive destruction across much of what is now modern-day India, decimating vast swathes of ancient forests and pushing early human populations to the edge of extinction.

Scientists at the University of Illinois say that their results powerfully corroborate one of the most controversial theories in the natural sciences "” the Toba Catastrophe Theory.

The theory "” first proposed by Stanley H. Ambrose of the University of Illinois at Urbana-Champaign in 1998 "” holds that the supervolcanic event at Lake Toba intensified Earth's last ice age by releasing so much ash into the atmosphere that sunlight was blocked out for six years.  As global temperatures dropped by an average of 28 degrees Fahrenheit, the planet plunged into one its most bitterly cold periods of the last million years. 

Ambrose theorized that the crises brought on a severe evolutionary "bottleneck," reducing the entire human population to between 5,000 and 10,000 individuals and driving several other human-like hominid species to extinction.  According to the theory, this vast reduction in the number of humans helps explain the relatively modest genetic diversity present in humans today.

For the recently released study, Ambrose assembled a team of researchers to look for evidence supporting his theory from two different sources.

The team first collected and analyzed pollen samples from a marine core in the Bay of Bengal off the coast of India.  Some of the ancient pollen grains were imbedded in a layer of ash left over from the Toba eruption, while other samples were taken from above and below it.

Researchers also collected soil samples from both above and below the fossilized layer of ash in order to compare carbon isotope ratios.  Because areas with dense forests leave behind different ratios of carbon isotopes that grasslands, researchers were able to compare the samples and come up with a picture of the kind of vegetation that was present in the region both before and after the super-eruption.

Tests on the samples "” taken from three different regions of India "” showed that the Toba eruption initiated a distinct change in vegetation throughout the country.

The scientists discussed their results in a recent edition of the scientific journal Palaeogeography, Palaeoclimatology, Palaeoecology, saying that results of the pollen analysis indicated a reduction in the number of ferns "” which grow primarily in humid conditions "” while the carbon isotope tests revealed a pattern of more "open vegetation" after the eruption.  All of this, they wrote, "would suggest significantly drier conditions in this region for at least 1,000 years after the Toba eruption."

As Ambrose and his colleagues point out, dryness is indicative of cooler temperatures "because when you turn down the temperature you also turn down the rainfall."

"This is unambiguous evidence that Toba caused deforestation in the tropics for a long time," the researchers explained in summary.

Ambrose also suspects that the catastrophe may have forced our early human ancestors to engage in a greater degree of social networking in order to develop cooperative strategies for surviving the hard times.

The adaptive social strategies acquired during the crisis would have then permitted our homo sapiens forerunners to overtake more physically robust yet less intelligent hominid species like Neanderthal.

And the rest, as they say, is history.


Image Caption: Illustration of what the eruption might have looked like from approximately 50 miles (80 km) above Pulau Simeulue. Courtesy Wikipedia


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