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Prehistoric World

Climate Change marks the Dawn of Man

Edited from BBC News, 19 August 2005

Complex variation of the East African climate may have played a key role in the development of our human ancestors.

Scientists wer able to identify 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 were reported in the Science journal. They suggested 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 which contained microscopic algae skeletons, called diatoms, revealed the depth and composition of the ancient lakes. Volcanic ash in nearby layers provided an estimate of the lakes' ages. Radioactive elements in the ash acted as time stamps because they decay in a predictable way over 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 argued that the growth of these lakes resulted from a moist local climate. The regional wet periods, which may have persisted for up to a hundred thousand years, occurred as much of Africa became increasingly dry.

The periods of wet weather in East Africa may reflect fluctuations of the Earth's climate as a whole. At the time at which the lakes grew - roughly 2.6 million, 1.8 million, and one million years ago - glaciers and the atmosphere were also going through major transformations.

Emergence of humankind

The Science journal paper stated that if the lakes were temporary features which were related to the global climate, as the data suggested, then they provided strong support for theories in which early human species evolved and spread out in response to a rapidly changing environment.

'These episodes could have had important impacts on the speciation and dispersal of mammals and hominins,' the researchers wrote at the time.

Chris Stringer, then a leading researcher on early humans in the department of palaeontology at London's Natural History Museum, praised the quality of the data, saying that it provides 'very good evidence' of climate change in East Africa.

However, he stressed that more detailed work was necessary to positively link these environmental changes to the emergence of man.

'What this is showing is that there are fluctuations of the climatic belts moving up and down,' he said. 'But if early humans are able to move around, the effect of varying environment is reduced. The key issue now is how mobile are these people?'

 

 

     
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