The delta smelt and the East African Rift Valley

Dry winters spell trouble, in California today and in the cradle of humanity, 100,000 years ago


Andrew Leonard
September 5, 2007 7:51PM (UTC)

Another dry winter in California could lead to mandatory water conservation, the San Francisco Chronicle reported Wednesday. Water officials are warning that continued drought conditions, in combination with a federal judge's decision to protect the infamous delta smelt by setting limits to the amount of water that can be pumped out of the San Joaquin-Sacramento River Delta, spell potential doom for suburban lawns in northern California.

For How the World Works, the news engendered a sense of solidarity with the small band of humans who lived many thousands of years ago in East Africa and from whom all of humanity is believed to be descended. New research reported this week in the Proceedings of the National Academy of Sciences provides the most detailed evidence yet of a series of megadroughts that occurred between 70,000 and 145,000 years ago and that may have had substantial impact on the expansion and migration of early modern human populations. (Thanks to Mongabay for the tip.)

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The bulk of the PNAS paper deals with the nitty gritty details of analyzing drill cores from Lake Malawi in the East African Rift Valley. Lake Malawi is one of the world's deepest and oldest lakes; it's "lacustrine deposits" provide remarkably detailed climate records that go back almost a million years. If you're the kind of geek who grooves on the mysteries posed by "biostratigraphic anomalies," this paper's for you.

Only a few paragraphs are devoted to the potential implications for humanity. The theory appears to be that the megadroughts may have had a devastating impact on the local ecology, making survival for all kinds of animals difficult. But about 70,000 years ago, the climate got much wetter, and humanity started its long road to complete world domination, (and an eventual showdown with the delta smelt.)

The team of researchers, led by Syracuse geologist Christopher Scholz, are careful in presenting their conjecture.

Before 70 kyr ago, the tropical lake data sets indicate a period of heightened climate variability, when tropical refugia expanded and collapsed repeatedly. Whether a series of climatic crises before 70 kyr ago produced a true human population bottleneck is still uncertain (47). The question arises as to whether the observed change to a more hospitable climate after 70 kyr ago, the dramatic late-Pleistocene population expansion, and the only successful early-modern human African exodus are mere coincidence.

Coincidence? How the World Works thinks not, but then again, we've always been sucker for climate-change-alters-human-history conspiracy theories. It's seems pretty much a no-brainer that a megadrought can really mess things up.

Which is just one more reason to keep an eye on the delta smelt, and maybe flush the toilet a little less often.


Andrew Leonard

Andrew Leonard is a staff writer at Salon. On Twitter, @koxinga21.

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Environment Global Warming Globalization How The World Works

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