Sediment cores collected from Africa's Rift Valley suggest the cradle of humanity's climate was characterized by long droughts punctuated by brief periods of rain.

In a new study, published this week in the journal Proceedings of the National Academy of Sciences, scientists argue the region's variable climate spurred early human evolution some 500,000 years ago.

The survey of sediment cores extracted from the rift valley basins of southern Kenya is one of the first to offer paleoclimatic context to the region's rich archaeological record.

When researchers compared their analysis of ancient sediments with archaeological and paleontological records, they found a correlation between regional climate patterns, animal extinctions and significant shifts in stone tool technology.

"Much evidence for human evolution has been gathered from the area, but linking those records to detailed environmental records was missing until now," Richard Owen, researcher at Hong Kong Baptist University, said in a news release. "There is a big gap in the records between the last Early Stone Age tools 500,000 years ago and the appearance of Middle Stone Age tools about 320,000 years ago. Our results plugged that gap with a continuous environmental record."

The gap has previously yielded evidence of an advancement in early humans' ability to make and use stone tools. Researchers have also uncovered evidence early human populations traded technological innovations.

Now, scientists have evidence that the Olorgesailie region was characterized by an increase in drought and climate variability during the period.

"The older stone tools found at Olorgesailie did not change much between 1.2 million and a half-million years ago," said Andrew Cohen, a professor at the University of Arizona. "And suddenly, after 500,000 and before 320,000 years ago -- we don't know exactly when, but in that timespan -- there was a critical transition in archeology when tools became more sophisticated and were transported over longer distances."

Researchers hypothesize the pressures of climate variability and drought put a premium on the ability of early humans to adapt. The bigger, more capable brains of Homo sapiens proved advantageous.

"Now we have evidence that at the same time the toolkits were changing, the mammal fauna changed and the climate became more arid," Owen said. "So you have a series of coincidences that makes you think, 'This could be real.' Now we can say when the environment changed and then compare that to the archeological evidence of the region."

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