Ancient cave formations found in Israel provided the first
concrete evidence that climate change allowed early humans to
migrate out of Africa, according to researchers in 2007.
A team of Israeli scientists studied stalactites and
stalagmites, or speleothems, which had been found in five caves deep in the Negev
Desert in southern Israel. They found that the growth patterns of the formations, which only develop in the
presence of rain water, revealed a major cluster of unusually rainy
periods beginning some 140,000 years ago.
The rainy spells matched the period which saw the first modern human
settlements in the Middle East. The scientists found that the period of enhanced rainfall
which allowed the
growth of speleothems occurred roughly between 140,000 to 110,000 years
ago, with its height being 130,000 to 125,000 years ago.
These dates correspond with modern human settlements
which have been 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 ago. The wet periods formed what, essentially, were climatic windows
that allowed migration north through the Sahara and up into Asia via
a 'land bridge' on the Sinai Peninsula.
The desert began to shrink both from the south and also from
the north. 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 the
Israeli team, the wet seasons reflected in the formations
most likely helped ancient humans to pass through the otherwise arid region. These monsoon rains strengthened the Nile's
flow, forming a northbound 'highway'.
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 to
see 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.