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This is

is Scientific Americans 60 Second Science. I'm Christopher

and Tagyatta.

10,000 years ago, the Sahara had extensive grasslands and was dotted with lakes and trees.

But some 5,000 years ago, that green Sahara dried up to become the enormous desert we know today.

And scientists now think that this climate shift had

effects far away including causing a mega drought in Southeast Asia.

Kathleen R Johnson, a paleoclimatologist and geochemist at the University of

California Irvine

says the key to that discovery were stalagmites,

collected in a cave in northern Laos.

So likemites are really amazing archives of past climate variability.

People are often more familiar with things like tree rings or ice cores

or maybe ocean sediment cores.

While stalagmites work in a similar way

in that they are deposited over time.

Johnson's team analyzed trace elements and carbon and oxygen isotopes in the hardened cave

drippings.

That information enables researchers to determine rainfall patterns over the millennia.

...