Complex variation of the East African climate may have
played a key role in the development of our human ancestors.
Scientists have identified extensive lake systems which
formed and disappeared in East Africa between one and three million years
ago. The lakes could be evidence that global climate changes occurred
throughout this pivotal period in human evolution.
The findings, reported in the journal Science, suggest
that humans evolved in response to a variable climate. Dr Martin Trauth
of the University of Potsdam and his team were able to identify and
date the prehistoric lakes by studying layers of soil along the Rift
Valley in Kenya, Ethiopia, and Tanzania.
Exploring ancient lakes
Layers containing microscopic algae skeletons, called
diatoms, reveal the depth and composition of the ancient lakes. Volcanic
ash in nearby layers provides an estimate of the lakes' ages. Radioactive
elements in the ash act as time stamps because they decay in a predictable
way with time.
By examining soil layers at seven sites throughout East
Africa, Dr Trauth and his collaborators were able to identify three
distinct periods during which extensive lakes covered the region and
grew to depths of hundreds of metres.
They argue that the growth of these lakes resulted from
a moist local climate. The regional wet periods, which may have persisted
for up to 100,000 years, occurred as much of Africa became increasingly
The periods of wet weather in East Africa might reflect
fluctuations of the Earth's climate as a whole. At the time at which the
lakes grew - roughly 2.6, 1.8, and one million years ago - glaciers
and the atmosphere were also going through major transformations.