Sunday, October 19, 2008

Dates from China show early hominins left Africa 1.8 MYA

Over a million years ago, a band of early humans left their stone
tools and two front teeth near a stream in southwest China. This find
indicates that early humans left Africa 1.8 million years ago.

For decades, the precise age of the fossils has remained a mystery,
leaving open a central question in paleontology that how quickly
did our human ancestors reach China after leaving Africa?

Now, thanks to advanced dating techniques, scientists may finally
have the answer. Although the original hillside where the fossils
were found has been excavated, the discoverers recorded the layer
of sediment where they uncovered the teeth and tools.

The new team traced that sediment layer - or time horizon - throughout
the basin, collecting 318 rock samples from it. Now, a team of Chinese
and American researchers has redated the Yuanmou Basin site using
a paleomagnetic technique that relies on rock samples to determine
the direction of Earth's magnetic field when the rocks were formed.

Chinese paleontologists discovered the two incisors in 1965 and the
relatively simple stone tools in 1973 in the Yuanmou Basin.

The teeth came from a hominin, the group that includes humans and our
exclusive ancestors, and might be from the species Homo erectus,
a direct ancestor of humans that may have been the first human to
spread beyond Africa about 1.8 million years ago.

Lacking solid dates, researchers thought until a decade ago that
the earliest humans didn't reach Asia until 1 million years ago.
But a series of dates for fossils from one site in Java, Indonesia,
in particular, have recently shown that Homo erectus was there 1.66
million years ago and possibly earlier.

This has changed the old textbook view that human ancestors spread around
the globe only after they had big brains and more advanced stone hand
axes, which appear in Africa about 1.6 million years ago.

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