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.
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."
The Nile became a highway
The researchers analysed the cave deposits using high-precision
spectrometry to measure their periods of growth.
According to Vaks, the wet seasons reflected in the formations
likely helped ancient humans pass through the otherwise arid region.
"These monsoon rains strengthened the Nile's flow, forming a
northbound 'highway,'" Vaks said.
"The climate along the shoreline of the Red Sea was also much
less extreme during this period, and archaeologists have found
evidence of migration along the coasts."
"It is reasonable that there is a connection between a wet
period along the Sinai-Negev land bridge and the appearance of early
modern man for the first time outside of Africa," he added.