Re: Homo came from Asia?
- From: Marc Verhaegen <m_verhaegen@xxxxxxxxx>
- Date: Sun, 12 Oct 2008 13:28:58 +0200
http://www.sciencedaily.com/releases/2004/10/041001092127.htm
Southern exodus. A trail of stone tools and fossil bones suggests that early
humans left Africa 1.8 million years ago. Some headed north to Dmanisi,
Georgia; others may have taken a southern route into China and Java,
Indonesia.
Ann Gibbons 7.10.08 ScienceNOW
http://sciencenow.sciencemag.org/cgi/content/full/2008/1007/3?etoc
Over a million years ago, a band of early humans left their stone tools and
two front teeth near a stream in southwest China. For decades, the precise
age of the fossils has remained a mystery, leaving open a central question
in paleontology: How quickly did our human ancestors reach China after
leaving Africa? Now, thanks to advanced dating techniques, scientists may
finally have the answer.
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. Scientists have gotten mixed results for the age of the site
because there were no volcanic crystals in the soils for reliable
radiometric dating. 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 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.
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. 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. In
an article in press in the Journal of Human Evolution, the researchers
report that the fossils came from a layer of rock just above a magnetic
landmark known as the Olduvai-Matuyama reversal boundary, which is at least
1.77 million years old. This makes the fossil site slightly younger, about
1.7 million years old.
This age estimate represents "the oldest definite fossil and archaeological
evidence of early hominins in China and mainland East Asia," says co-author
Rick Potts, a paleoanthropologist at the Smithsonian Institution in
Washington, D.C. The finds are a bit younger than the oldest Homo erectus
fossils from western Asia, which are 1.77 million years old and come from
Georgia, and a bit older than the most conservative dates for the Java
remains and 1.66-million-year-old stone tools from northeast China. Taken
together, these dates from at least three fossil sites are convincing many
researchers that early humans were moving rapidly across Asia 1.77 million
to 1.66 million years ago. "What's so important about this paper is that we
finally have good, solid paleomagnetic dates," says paleoanthropologist
Susan Antón of New York University in New York City. "I think the body of
data for early Homo in China is getting much stronger."
.
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