http://www.spacedaily.com/news/life-01zp.html
Mass Extinctions May Be A Myth, Claim Scientists
London - Nov 13, 2001
Catastrophic mass extinctions, such as the one that saw the demise of the
dinosaurs,could be a myth according to the findings of recent research into
100 million-year-old marine fossils.
It is widely believed that there has been about a dozen mass extinctions
during the history of life on Earth, the most devastating of which saw 84%
of the planet's species disappear.
But research by geologist Professor Andy Gale of the University of Greenwich
and palaeontologists from the Natural History Museum, published recently in
the American journal Paleobiology, is now casting doubt upon whether these
mass extinctions took place.
"Large gaps in the fossil record are often cited as evidence of mass
extinctions. But there are other explanations for this lack of fossil
evidence which do not point to a catastrophic annihilation of large numbers
of species, says Professor Gale.
"During the Cretaceous period (146 to 65 million years ago), dominated by
dinosaurs, there were periods of intense global warming which saw dramatic
rises in sea levels so severe that the oceans flooded Europe, turning it
into an archipelago of little islands. This forced shallow marine species
and land animals to migrate from their usual habitats.
"Once the sea level dropped again these species migrated back with it, and
the fossil record laid down in sedimentary rock during those periods of high
sea level was largely destroyed over time by wind, rain and glacial
erosion," continued Professor Gale.
"The interruption in the fossil record during these periods was caused by
species migration and the loss of the fossil record of that migration, and
not by a mass extinction."
Evidence of these "pseudoextinctions" can be seen in the fossil record of
the chalk cliffs at Dover in Kent and Beachy Head on the Sussex coast. Many
of the shallow water organisms which disappeared from the fossil record in
these cliffs, 100 to 95 milllion years ago, reappeared millions of years
later when sea levels fell.
"It initially appears from the fossil record contained within these cliffs
that marine species during this period suffered extinction rates of up to
70%," says Professor Gale.
"But the reality is that the reappearance of the majority of these species
indicates that they were simply displaced to other areas by rising sea
levels, and then returned, without suffering significant extinction. Taking
this into account, the extinction rate during this period falls to 17%, a
level that inevitably occurs at any time.
"Based on the fossil evidence we have analysed, we believe that there was no
mass extinction 100 million years ago, as previously thought," concludes
Professor Gale.
"It is also probable that many of the other mass extinctions that were
thought to have taken place during the history of life on Earth either did
not happen or have been greatly exaggerated."
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