By David
Derbyshire, Science Correspondent
Electronic Telegraph
THE
northwards drift of Australia and New Guinea three million years ago brought droughts
to Africa, ice sheets to Europe and may even have shaped the evolution of our
ancestors.
Researchers investigating the role of tectonic plate movement
on climate believe they can explain the change in weather systems at a crucial
stage in human evolution.
Previous studies have suggested that the closing
of the Panama Isthmus, changed the flow of warm water around the Pacific and brought
arid weather to Africa at a crucial time in human evolution.
But by studying
the northward migration of the Australian plate towards South-East Asia, a team
of American scientists believes that they have come up with an alternative explanation.
Up
to three million years ago there was still enough open water between New Guinea
and Asia to allow warm water to flow west from the South Pacific into the Indian
Ocean. The warmer sea surface temperatures in the Indian Ocean brought high levels
of rainfall over East Africa, the scientists report in Nature.
But as the
Australian plate moved northwards, this gateway between the oceans became too
narrow and too shallow. The closing of this Indonesian seaway increased the influence
of colder water coming from the northern Pacific. As the Indian Ocean cooled,
East Africa became drier.
The researchers, led by Dr Marck Cane of Columbia
University, Palisades, also believe that the changing ocean currents triggered
the start of the ice-age cycles.
The drying of Africa came during the era
of Australopithecus afarensis, one of the first branches of the human family tree
to emerge after the split from chimpanzees five million years ago. The new drier
climate would have seen the growth of grassland plains and deserts and the loss
of forests across parts of Africa.
The relatively rapid period of climate
and habitat change is likely to have had a major effect on the evolution of these
ancestors into more human-like species, the researchers say. |
