Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Newfound Ancient African Megadroughts May Have Driven Evolution Of Humans And Fishes

09.10.2007
From 135,000 to 90,000 years ago tropical Africa had megadroughts more extreme and widespread than any previously known for that region, according to new research.

Learning that now-lush tropical Africa was an arid scrubland during the early Late Pleistocene provides new insights into humans' migration out of Africa and the evolution of fishes in Africa's Great Lakes.

"Lake Malawi, one of the deepest lakes in the world, acts as a rain gauge," said lead scientist Andrew S. Cohen of The University of Arizona in Tucson. "The lake level dropped at least 600 meters (1,968 feet) -- an extraordinary amount of water lost from the lake. This tells us that it was much drier at that time."

He added, "Archaeological evidence shows relatively few signs of human occupation in tropical Africa during the megadrought period."

The new finding provides an ecological explanation for the Out-of-Africa hypothesis that suggests all humans descended from just a few people living in Africa sometime between 150,000 and 70,000 years ago.

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

Other researchers have documented droughts in individual regions of Africa at that time, such as the Kalahari desert expanding north and the Sahel expanding south, he said. "But no one had put it together that those droughts were part of a bigger picture."

Tropical Africa's climate became wetter by 70,000 years ago, a time for which there is evidence of more people in the region and of people moving north. As the population rebounded, people left Africa, Cohen said.

The newly discovered drastic drought also suggests the famous cichlid fishes of Lake Malawi evolved four to eight times slower than previously thought and alters scientists' view of fish evolution in the African Great Lakes.

The research article by Cohen, UA researchers Jeffery Stone, Peter Reinthal and David Dettman and colleagues, "Ecological consequences of early Late Pleistocene megadroughts in tropical Africa," is scheduled for early online publication the week of Oct. 8 in the Proceedings of the National Academy of Sciences. Another article by members of the Lake Malawi Drilling Project, "East African megadroughts between 135 and 75 thousand years ago and bearing on early-modern human origins," is online at the Proceedings of the National Academy of Sciences. Christopher Scholz of Syracuse University in N.Y. is first author and Cohen and others are co-authors.

Both articles are scheduled for publication in the Oct. 16, 2007, print edition of the Proceedings of the National Academy of Sciences. A full list of authors for each article is at the end of this release. The National Science Foundation, the International Continental Drilling Program and the Smithsonian Institution funded the research.

Cohen and his colleagues have been working for years to learn more about ancient Africa's climate and ecology by coring Africa's deepest lakes.

The scientists discovered the ancient megadroughts by studying sediments cored from the bottom of Lake Malawi, an African rift lake that is currently 2,316 feet (706 meters) deep, and comparing those findings with similar records from Lakes Tanganyika and Bosumtwi.

"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.

Extracting cores from Lake Malawi required the kind of rig used in ocean-going drilling expeditions. Those expeditions just sail a drill-equipped ship to the desired site.

However, the Lake Malawi Drilling Project's target was a land-locked lake.

The international research team collected the equipment necessary, shipped it overland, rented a barge and outfitted it to become a scientific drilling vessel. They equipped the ship, M/V Viphya, with the type of GPS positioning system needed to hold the large ship steady under windy and wavy conditions as the drilling equipment was lowered 1,942 feet (592 meters) to the lake bottom and bored into the lake's sediment another 415 feet (380 meters). If the ship didn't hold its position over the drilling site, the expensive drilling equipment might snap.

The work was successful -- the team extracted a series of cores, some as much as
415 feet (380 meters) long, representing hundreds of thousands of years of African history.

The researchers used radiocarbon and other dating techniques to establish the age of regions of the core. Then researchers took samples at 300-year-intervals.

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.

Samples from the megadrought times had little pollen or charcoal, suggesting sparse vegetation with little to burn.

"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," Cohen said.

One indicator of drought present in the cores were species of invertebrates and plankton that only live in shallow, turbid, algae-rich waters -- a situation very different from the deep, clearwater lake that Malawi is now.

"During the megadrought, Lake Malawi was algae-filled and pea-soup green, much like modern-day Lake Turkana," Cohen said. "Lake Turkana is known as the Jade Sea."

The African Great Lakes are known for the spectacular biological diversity of their cichlid fish species, which number in the hundreds. A dramatic increase in the number of species was thought to happened after a dry spell about 25,000 to 15,000 years ago.

In contrast, Cohen and his colleagues suggest that the rise in species diversity happened after the megadroughts. By 70,000 years ago the lake had risen to more or less its current level and it had become a freshwater lake as it is today.

Although the team has used the lake cores to peer back in time 150,000 years, there's still much more to do: the Lake Malawi core represents as much as 1.5 million years of tropical Africa's past.

Cohen's co-authors on "Ecological consequences of early Late Pleistocene megadroughts in tropical Africa" are David Dettman and Peter N. Reinthal of The University of Arizona; Jeffery R. Stone of The University of Arizona and the University of Nebraska at Lincoln; Kristina R. M. Beuning and Sarah J. Ivory of the University of Wisconsin-Eau Claire; Lisa E. Park of the University of Akron in Ohio; Christopher A. Scholz of Syracuse University in N.Y.; Thomas C.

Johnson and Erik T. Brown of the University of Minnesota, Duluth; John W. King of the University of Rhode Island at Narragansett; and Michael R. Talbot of the University of Bergen in Norway.

Cohen's co-authors on "East African megadroughts between 135 and 75 thousand years ago and bearing on early-modern human origins," are Christopher A. Scholz and Robert P. Lyons of Syracuse University in N.Y.; Thomas C. Johnson, Erik T.
Brown and Isla S. Castaneda of the University of Minnesota, Duluth; Jonathan T.
Overpeck and Timothy M. Shanahan of The University of Arizona; John W. King and Clifford W. Heil of the University of Rhode Island at Narragansett; John Peck of the University of Akron, Ohio; Michael R. Talbot of the University of Bergen in Norway; Leonard Kalindekafe of the Malawi Geological Survey Department in Zomba; Philip Y. O. Amoako of the Geological Survey Department of Ghana in Accra; Steven L. Forman, Jeanette Gomez and James Pierson of the University of Illinois at Chicago; Lanny R. McHargue of the Scottish Universities Environmental Research Centre in East Kilbride; and Kristina R. Beuning of the University of Wisconsin-Eau Claire.

Mari N. Jensen | University of Arizona
Further information:
http://malawidrilling.syr.edu/
http://www.arizona.edu
http://www.geo.arizona.edu/web/Cohen/AC_page.html

More articles from Earth Sciences:

nachricht Ice cave in Transylvania yields window into region's past
28.04.2017 | National Science Foundation

nachricht Citizen science campaign to aid disaster response
28.04.2017 | International Institute for Applied Systems Analysis (IIASA)

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Making lightweight construction suitable for series production

More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.

Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...

Im Focus: Wonder material? Novel nanotube structure strengthens thin films for flexible electronics

Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.

"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...

Im Focus: Deep inside Galaxy M87

The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.

Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...

Im Focus: A Quantum Low Pass for Photons

Physicists in Garching observe novel quantum effect that limits the number of emitted photons.

The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...

Im Focus: Microprocessors based on a layer of just three atoms

Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.

Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Fighting drug resistant tuberculosis – InfectoGnostics meets MYCO-NET² partners in Peru

28.04.2017 | Event News

Expert meeting “Health Business Connect” will connect international medical technology companies

20.04.2017 | Event News

Wenn der Computer das Gehirn austrickst

18.04.2017 | Event News

 
Latest News

Wireless power can drive tiny electronic devices in the GI tract

28.04.2017 | Medical Engineering

Ice cave in Transylvania yields window into region's past

28.04.2017 | Earth Sciences

Nose2Brain – Better Therapy for Multiple Sclerosis

28.04.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>