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Ancient cave formations found in Israel provide the first concrete evidence that climate changes allowed early humans to migrate out of Africa, researchers say.
A team of Israeli scientists studied stalactites and stalagmites, or speleothems, found in five caves deep in the Negev Desert in southern Israel (see Israel map).
The growth patterns of the formations, which only develop in the presence of rainwater, revealed a major cluster of unusually rainy periods beginning some 140,000 years ago, the scientists said.
The rainy spells match the period of the first modern human settlements in the Middle East, the team added.
"We found that the period of enhanced rainfall allowing the growth of speleothems occurred roughly 140,000 to 110,000 years ago, with its height being 130,000 to 125,000 years ago," said Anton Vaks, a doctoral student with the Geological Survey of Israel (GSI) and the Hebrew University of Jerusalem.
These dates correspond with modern human settlements found slightly farther north in Israel's Carmel region and near Nazareth. Archaeological evidence has dated those sites to about 100,000 to 130,000 years old.
The wet periods formed what were essentially climatic windows that allowed migration north through the Sahara and up into Asia via a "land bridge" on the Sinai Peninsula, Vaks explained.
"The desert began to shrink both from the south and also from the north," he said.
"The entire Sahara turned into something much, much smaller, and the desert barrier [out of Africa] was much less significant."
Nile Became "Highway"
The researchers analyzed the cave deposits using high-precision spectrometry to measure their periods of growth.
The wet seasons reflected in the formations likely helped ancient humans pass through the otherwise arid region, Vaks said.
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