Posted on 12/08/2005 3:58:46 AM PST by TigerLikesRooster
Ancient drought 'changed history'
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The evidence comes from sediments drilled up from the beds of Lake Malawi and Tanganyika in East Africa, and from Lake Bosumtwi in Ghana. It shows equatorial Africa experienced a prolonged period of drought. It is possible, scientists say, this was the reason some of the first humans left Africa to populate the globe. Certainly, those who remained on the continent at that time would have had to be extremely resilient to make it through such hard times. "This was a profound impact on the landscape," said Christopher Scholz, from Syracuse University, US. "So it must have had a major impact, not just on humans but on all species in equatorial Africa at this time." Tight group Dr Scholz presented data from the drilling project here at the Fall Meeting of the American Geophysical Union. The cores reveal that prior to 75,000 years ago, Lake Malawi, which is currently an inland sea some 550km long and 700m deep, was reduced to a couple of pools no more than 10km across and 200m deep.
Only a prolonged continent-wide drought could have had this effect. What makes the timing so fascinating is that it ties in with the "Eve hypothesis" of human evolution. Genetic studies suggest modern human society is descended from a group of around 10,000 individuals who lived in East Africa at the time of this crisis. Immediately after its end, human populations started to expand rapidly - and many of our ancestors began moving out of Africa and into the Middle East, Asia and Europe. Driving force Scientists are increasingly convinced that tragedies in the deep past have shaped human evolution. The intriguing thought is that we owe our existence to a small band of survivors who clung on to life during a crisis of epic proportions or who simply decided they had to move to find water.
"And, also, there may be a connection with the exodus of early modern humans out of Africa and this climatic release. "There's been recognition that speciation of hominids is controlled by environmental factors - whether that's long-term changes in aridfication in Africa or perhaps the dramatic increase in variability in environmental conditions, such as in precipitation, temperature, and so forth." |
"The last glacial maximum 18,000 to 23,000 years ago."
There were a number of major volcanic events from 28 kya to 22 kya, that appeared to cause a stepwise decrease in temperatures. The one for 22,000 years ago was Mt. Sakura-jima in Japan. It left a crater 15 miles in diameter, which is now a great bay with a much smaller volcano of the same name on one side. I would love to get time and size data on a few other possible major volcanic events for that period.
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GGG managers are SunkenCiv, StayAt HomeMother & Ernest_at_the_Beach | |
Just updating the GGG info, not sending a general distribution.12,400 years ago? Hydrologic cycle came to a screeching whoa for some reason, hmm, what could it have been?Evolution in Your FaceLake Victoria, Africa's largest lake, is home to more than 300 species of cichlids. These fish, which are popular in aquariums, are deep-bodied and have one nostril, rather than the usual two, on each side of the head. Seismic profiles and cores of the lake taken by a team headed by Thomas C. Johnson of the University of Minnesota, reveal that the lake dried up completely about 12,400 years ago. This means that the rate of speciation of cichlid fishes has been extremely rapid: something on average of one new species every 40 years! |
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