Popular theory of ‘volcanic winter’ killing early humans is at the centre of debate over climate and evolution

28-Sep-2020 Intellasia | South China Morning Post | 6:02 AM Print This Post

The last eruption of the Toba volcano was about 74,000 years ago in northern Sumatra, Indonesia.

Up to 3,000 cubic kilometres of mass were thrown up, releasing an amount of energy equivalent to 300,000 Hiroshima bombs.

According to a prevailing theory, the Toba eruption caused a “volcanic winter” that wiped out early humans, sparing only a few lucky survivors in Eastern Africa, who became the direct ancestors of every human being today.

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A recent study by a team of Chinese palaeoanthropologists found theory, which has captured the public imagination for more than two decades with “tantalising simplicity”, could be rubbish.

“It is time to relegate this hypothesis to the dustbin of history,” said the researchers led by Professor Gao Xing of the Institute of Vertebrate Palaeontology and Palaeoanthropology at the Chinese Academy of Sciences in Beijing, in a peer-reviewed-paper published in the journal Quaternary International in July.

Gao and colleagues analysed geological data and fossil records collected in China and other parts of the world in recent years. They found no evidence of abrupt disruption to human activities during and after the eruption of Toba. In China, Europe or even India, life appeared to continue without apparent interruption, according to Gao and his colleagues.

The severity of climate change caused by the volcanic eruption could be considerably less than previously thought, too.

These findings called for “a more rational and objective view of palaeoclimatic changes and the origin and evolution of modern humans,” said the Chinese researchers.

In northern China, toolmaking activities persisted until 40,000 years ago. In some archaeological sites over southern China, the palaeolithic industries went on even further with pebble tools made with continuous fashion and techniques.

DNA analysis of ancient human remains also suggested that some early human species, such as Neanderthals, Denisovans, Homo floresiensis and the small-bodied Homo luzonensis, continued to live after the Toba catastrophe across the world.

This happened “even in the area very close to the Toba crater,” Gao said in the paper.

Richard G. Roberts, professor of archaeology at the University of Wollongong in Australia, supported the opinions of the Chinese researchers.

The Toba super-eruption would have been catastrophic for people, animals, plants and the landscape in northern Sumatra at the time of explosion, said Roberts, who was not involved in the Chinese study.

On the basis of current evidence, however, the event did not “cause a ‘volcanic winter’ of serious extent or duration, despite its huge size,” Roberts told the South China Morning Post.

The Chinese team said some previous studies might have overestimated the impact of the Toba eruption on global climate because some crucial elements were not considered.

The vapour generated by heat, for instance, might have significantly reduced the amount of dust that reached the high atmosphere.

The Earth’s position relative to the sun then was also different from today, with hotter summers and colder winters. The sunlight-blocking particles in the atmosphere might have served as a blanket to keep in more heat in winter, thus limiting the overall drop of the average temperature throughout the year, said the Chinese team.

However, on the Chinese team’s findings that climate change could have been less severe than previously thought, Professor Alan Robock, a renowned climatologist at Rutgers University in the United States, said the researchers got it wrong.

Robock said their simulation found that instead of water vapour inhibiting the formation of sulphuric acid droplets, would help produce a large cloud.

And if the winter warming effect did occur, it would have affected only part of the Earth but not the tropics, where there was no winter, according to Robock, father of the famous “nuclear winter” theory.

The Chinese team had also failed to provide data with annual resolution in terms of climate response, so they could not rule out the possibility of several years or a decade of extreme cooling from the eruption,” he said.

“It is really a shame that this paper did not have a reviewer who understood climate physics, who could have corrected all of this,” Robock said.

Genetic analysis suggested that the ancestors of human beings walked out of African about 70,000 years ago. It took them about 10,000 years to reach southern China.

Wherever they went, the locals disappeared. Why that happened remained a mystery.

“Other major environmental changes independently took place around the same time at the Toba eruption, including a period of several thousand years of generally cooler global temperatures,” said Roberts.

“Also, various types of interactions within and between different groups of humans could have triggered population bottlenecks,” he said. “It is rarely one thing or another, but a combination of factors.”



Category: Indonesia

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