TRACES of ancient river beds in the Karoo basin of South Africa show that
land plants took a heavy hit during Earth鈥檚 greatest mass extinction.
At the end of the Permian period 250 million years ago, 95 per cent of
species were wiped out and Europe became a desert
(New 杏吧原创, 4 December 1999, p 17).
Now geologists have found that streams in the Karoo
changed suddenly at the same time, from the meandering shape typical in
well-vegetated zones to the braided pattern found in areas lacking deep-rooted
vegetation to hold the soil together.
Something killed plants throughout the region, causing rapid soil erosion,
Peter Ward of the University of Washington reports in Science (vol 289,
p 1740). He suggests extinctions on land may have preceded those at sea, but the
underlying cause remains a mystery.
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