"Mega-Drought" shaped human development

Lake sediments provide crucial evidence for a dramatic dry period

Algae rich, finely structured clay deposits from humid times (above) and gray, carbonaceous sediments from the drought (below). © Lake Malawi Drilling Project.
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About 100, 000 years ago, Africa was plagued by tens of thousands of years of drought, which brought the early humans of that time to the brink of extinction and eventually even started their migration out of Africa. Using drilling cores from Lake Malawi, American researchers gained this and other new insights into African history.

Scientists at the University of Arizona, led by Andrew S. Cohen, have been working for years to learn more about the climate history and ecology of Africa's past. Their most important tools for this are drilling cores from the sediments of the African lakes. The goal of their current campaign was to compare the previously harvested cores from Lake Tanganyika and Lake Bosumtwi with new cores from Lake Malawi. "The unique thing about the cores from these three lakes is that they are end-to-end evidence, " explains Cohen. "We can trace from them what happened in these places a very long time ago."

Using equipment normally used in drilling on the high seas, they were able to recover several 380-meter-long cores from Lake Malawi's lake sediment. They represent hundreds of thousands of years of African climate history. Scientists analyze the pollen preserved in the rock, organic remains, seaplankton shells, and date the finds using the radiocarbon method. Their findings have now been published in the journal Proceedings of the National Academy of Sciences.

Dramatic loss of water indicates mega-drought

It turned out that tropical Africa must have lived through an extreme dry period between 135, 000 and 90, 000 years ago. In the samples samples from this period were hardly pollen or other vegetation remnants and also the lake itself showed signs of drought. The scientists found fossil plankton remnants in the cores, which are typically typical of shallow, algae-rich waters - and thus extremely untypical for the deep, very clear Lake Malawi.

"The Lake Malawi, one of the deepest lakes in the world, acts like a rain gauge, " explains Cohen. "The water level in the lake dropped by at least 600 meters - an extraordinary loss of water for this lake. This shows us that it was much drier then. Moreover, archaeological findings show very few signs of human habitation during the mega-drought period. "The region around Lake Malawi, today a dense tropical jungle, must have been more like a barren desert landscape at the time. display

D rre as a trigger for great human migration?

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The new findings may also explain why our ancestors, whose origins are in Africa, have suffered a sudden collapse of their populations between 150, 000 and 70, 000 years ago. We have an explanation of why this could have happened tropical Africa was exceptionally dry about 100, 000 years ago, Co said Cohen. "Human populations may have collapsed."

Previously, other scientists had identified periods of drought in certain areas of Africa during this period, including the Kalahari desert and the Sahel. "But no one has come to the conclusion that these dangers are part of a larger connection." Only about 70, 000 years ago did the climate begin to recover, it became moister. At the same time, there are indications of returning friars and recovering populations. However, as soon as the population began to recover, people began to migrate northwards, eventually leaving the continent.

New light on Africa's cichlids

And the story of the famous cichlids of the African lakes, whose biodiversity is a treasure trove for evolutionary researchers, appears in a new light through the new discovery of D rre. So far, the scientists suspected that occurred around 25, 000 to 15, 00 years, a huge boost in biodiversity. But Cohen and his colleagues think that this "arsenal explosion" must have happened much earlier, after the great drought period 70, 000 years ago. At that time, the lake filled up again and became the deep clear-water lake that it still has today.

This is a crucial difference for evolutionary research, as it would mean that biodiversity will not develop extremely fast, as previously thought, but four to eight times slower.

(University of Arizona, 09.10.2007 - NPO)