African Mega-Drought Rewrites Human Origins

Scientists who have been studying sedimentary cores from Africa's Lake Malawi have discovered that, 135,000 to 90,000 years ago, areas of the continent that would now be classified as tropical – such as Lake Malawi – were hit by a mega-drought. These droughts were so extreme and subsequently widespread that they were unlike anything the region had ever encountered previously.

The importance of this discovery lends new weight to the “Out of Africa” model for human evolution, also known as the Recent Single Origin Hypothesis.

Lake Malawi, the third largest lake in Africa and the ninth largest in the world, is situated between Malawi, Mozambique, and Tanzania, and the most southerly lake in the Great African Rift Valley system -long thought to be the birthplace of human evolution, where the bones of several hominid ancestors of modern humans have been found, including those of "Lucy" a nearly complete australopithecine skeleton, which was discovered by anthropologist Donald Johanson. The tropical waters of Malawi, also known as Livingston's Lake, after the famed British explorer, David Livingston ("I presume?") are inhabited with more fish species than any other lake on Earth.

The RSOH or Out of Africa hypothesis states that all human beings descended from one small evolutionary branch appearing in Africa between 200,000 and 100,000 years ago that then spread out from Africa 55,000 and 60,000 years ago.

"We've got an explanation for why that might have occurred -- tropical Africa was extraordinarily dry about 100,000 years ago," said Andrew S. Cohen, a University of Arizona in Tucson professor of geosciences. "Maybe human populations just crashed."

The Lake Malawi Drilling Project was responsible for providing sedimentary cores for the scientists to examine. The project was landlocked due to the depth at which they would have to be drilling; a slightest movement would snap the drills. And at 2,316 feet (706 meters) in depth, and drilling a further 1247 feet (380 meters) in to the sediment, snapping was a real possibility.

The team was able to essentially use the cores as a timeline for Africa. "What's unique about the Malawi, Tanganyika and Bosumtwi cores is that they're continuous records. We can see what happened in one place over a long period of time," Cohen said.

Such lake cores contain a high-resolution record of the things that fell in or died in the lake -- plankton, aquatic invertebrates, charcoal from fires on land, pollen from the surrounding vegetation. Scientists analyze those materials to figure out what the vegetation and the lake conditions were like at a particular point in time.

The samples that were taken during the mega-drought period – time determined by radiocarbon and other dating techniques – was found to have little pollen or charcoal, indicating that there was very little vegetation and even less that would burn.

Cohen said, "The area around Lake Malawi, which today is heavily forested and has rainfall levels comparable to the southeastern U.S., at that time would have looked like Tucson." In addition to ecological evidence, "Archaeological evidence shows relatively few signs of human occupation in tropical Africa during the mega-drought period,” added Cohen.

Comparably, 70,000 years ago there is recorded evidence for Africa being much wetter. In addition, there is evidence of more people in the region and of populated movement northwards.

This would suggest that when the human population in the area was provided with greener and wetter surroundings, they were once again able to breed without nature’s harsh winds and climates decimating their populations. With increased populations would naturally come the need to spread out and seek greener pastures, so to speak.

From there, the Out of Africa hypothesis springs, with populated movement tracked in to current locations such as North and South America, through Asia, and matched with the arrival of humans in Australia 50,000 years ago.

Posted by Josh Hill.

Story Links:

http://www.physorg.com/news111083381.html
http://www.timesonline.co.uk/tol/news/world/africa/article2617296.ece#cid=OTC-RSS&attr=1515793
http://en.wikipedia.org/wiki/Lake_Malawi
http://malawidrilling.syr.edu/
http://en.wikipedia.org/wiki/Recent_single-origin_hypothesis

Comments

[Mr. Bear]

I have heard that it was India's fault! Apparently, when the subcontinent crashed-into Asia and began rankling it, the Himalayan range that formed acted as a huge net for rain/clouds. The water that had been on its way to Africa instead fell upon India, and the rest is history. Nicely written.

[coop]

well some times a boat is your only ride

[coop]

well sometimes a boat is your only ride

[tyrome biggims]

i agree with mr.bear

[bond james bond]

i think that mr.bear is also correct hello there bear its your old college buddy