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Science Forum Index » Anthropology - Paleo Forum » Toba Super?Eruption...
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| Marc Verhaegen... |
 Posted: Wed May 07, 2008 1:07 pm |
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Ambrose et al.
Paleosol Carbonate and Pollen Evidence for Deforestation and Cooling in
South Asia Caused by the Toba Super?Eruption:
Implications for Human Evolution
The eruption of Toba, Sumatra, ~73,000 years ago was the largest explosive
eruption of the past two million years. Its impacts on global and regional
climate and on human evolution remain controversial. Ash from the Toba
eruption crops out as channel?fill and lake basin deposits across peninsular
India, and is present in marine sediment cores from the Indian Ocean, the
Arabian Sea and the East China Sea. Ice core records show that this eruption
marks a six?year?long volcanic winter, and the abrupt onset of a
1,800?year?long period of the coldest temperatures of the last 125,000
years. We present results of two independent lines of inquiry into the
impact of this eruption and instant ice age on ecosystems in India and
Sumatra. Pollen grains extracted from samples collected immediately beneath
and above the Toba ash in two marine cores, one west of Sumatra, the other
in the Bay of Bengal, show reduction of tree cover and cooling followed by
prolonged drought after the eruption. Stable carbon isotopes of fossil soil
carbonates directly beneath and above the Toba ash from three sites in the
Son and Narmada valleys of central India show forests before the eruption
and open or wooded grassland ecosystems after the eruption. Our results show
that the Toba eruption was followed by more than a millennium of drier and
cooler climate, with deforestation of some terrestrial ecosystems in South
Asia. We hypothesise that other tropical ecosystems may also have been
affected. Recent genetic bottlenecks and population subdivisions in humans
and other species, and extinctions of several SE Asian mammals, may have
been initiated by this event. The genetic structure of modern humans, the
course of modern human behavioral evolution, and dispersals out of Africa
may have been influenced by the environmental impact of the Toba eruption. |
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