Ancient drought 'changed history'

BBC ^ | 12/07/05 | Roland Pease

[TigerLikesRooster]

Ancient drought 'changed history'

By Roland Pease
BBC science unit, San Francisco

The sediments are an archive of past climate conditions

Scientists have identified a major climate crisis that struck Africa about 70,000 years ago and which may have changed the course of human history.

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.

Worse still was Lake Bosumtwi. Currently a 10km-wide lake that fills an old space impact crater, it lost all of its water.

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.

Viewed from space: Lake Bosumtwi is in an old impact crater

"We think there may be a connection between this climatic release - that is the rise in lake levels following this major desiccation event - and the order of magnitude increase in early modern humans," Dr Scholz said.

"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."

[JohnBovenmyer]

Dating is important as one major known catastrophic event happened at roughly that time. The most recent eruption of a super volcano, Toba in Indonesia happened about 75k years ago and blew a hole 60 by 18 miles wide and up to a mile deep there. Toba is by far the largest geologic event of the last 100k years. Shooting all that material into the atmosphere certainly messed up the world climate for several years. If this African drought happened right after Toba blew than look no further for its explanation. Also look no further than Toba for the reduced human population of that time that genetic research implies. It had to have a major effect on mankind at the time, but I don't think we have any human records, not even the legends of the Australian aborigines, that go back quite that far.

[Ciexyz]

btt

[Rocket1968]

Later read.

[blam]

"Also look no further than Toba for the reduced human population of that time that genetic research implies. It had to have a major effect on mankind at the time, but I don't think we have any human records, not even the legends of the Australian aborigines, that go back quite that far."

I agree. Probably Toba. I've seen estimates as low as 2,000 for the worldwide human population after Toba. Most are closer to 5,000 with some ranging up to 10,000. Even so, not many people for the whole world.

The Last Glacial Maximum(LGM) 18-23,000 years ago thinned out the human population dramatically too.

[VOA]

bump

[add925]

I'm a proud member of Haplogroup G2

[blam]

"However, IIRC, they felt the drought, due to an Ice Age, was comewhat more recent than 70,000 years."

See my post #24. It may have been the Last Glacial Maximum, the coldest period of the Ice Age.

[Elsie]

something on average of one new species every 40 years!

Or that fishy Gramma had been drinking wacky juice and squirted out ALL these critters herself!

---

(This assumin' is FUN! I'll have to do it more often!)

[Elsie]

The Last Glacial Maximum(LGM) 18-23,000 years ago thinned out the human population dramatically too.

Why??

I'da moved South!!!

[Elsie]

Glaciers locking up all the water so that streams and lakes go dry.....

[Straight Vermonter]

Glaciers locking up all the water so that streams and lakes go dry.....

Yes, but much more than that. The glaciers suck the moisture out of the air, which is how they grow. The area along the face of a giant glacier can be as dry as a desert.

[bigsigh]

I thought only historians and politicians could do that. : )

[neverdem]

ping

[expatpat]

The PBS program I referred to was talking about a drought and drop in sea-level that resulted from an Ice Age, when glaciers bound up a great deal of the water in the atmosphere and the oceans, forcing those in interior Africa like the clicking bushmen we are descended from to move.

[VadeRetro]

Maybe worth a look.

[PatrickHenry]

Very interesting. But it's probably a "Blam" thread more than it is one of ours.

Junior, archive?

[Junior]

Coitenly. The archive's an archive after all...

[JohnBovenmyer]

There have been lots of ice ages in history, but not many super volcano eruptions. When a dramatic drought falls reasonably close to the latter and PBS blames the former I get suspicious. There is loads of liberal angst regarding the former, but little regarding the latter. I guess they haven't figured out how to blame volcanoes on Bush yet. They'd love to have an ice age just to blame Bush for it. Absolute geologic dates c. 75k ago often are give or take a few thousand years. Sometimes data exists to compare one ancient event to another more precisely. I don't know if that exists here. If the drought closely followed Toba I'd blame Toba even if there was an ice age then. It wouldn't surprise me for Toba to have triggered an ice age itself. It put a lot more into the atmosphere than we and the Russians could have in nuclear war, yet the left loved scream about 'nuclear winter.'

[Elsie]

How'd we ever get from NW to GW???


Seems to me, if it gets too warm, all we gotta do is pop of a few nukes!!

[Cliff Dweller]

It shows equatorial Africa experienced a prolonged period of drought.

Al Gore just called. Turns out it was Global Warming that caused this. As the inventor off the internet, Al proclaims that this was a precursor event to show how bad things could get...

Unfortunately the oral history of the local inhabitants failed to carry the message accurately to the present day.(/sarc)