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Ocean EcoSystems Unexpectedly Stable
(Blacksburg, Va., May 14, 2002) -- Marine life had to re-evolve after two
major extinctions in order for shrimp and whales and other sea life as we
know it to come into being. But what is remarkable, according to an
article published in the May 14, 2002 issue of the Proceedings of the
National Academy of Sciences (PNAS), is not that marine life recovered
from two mass extinctions, but that marine ecosystems have maintained very
stable structure over the last 450 million years and only changed
noticeably in the recovery from these two great extinctions.
Previous studies claim five mass extinctions decreased the diversity of
ocean life. But the PNAS article, "Anatomical and Ecological Constraints
on Phanerozoic Animal Diversity in the Marine Realm," by Richard Bambach,
professor emeritus of geological sciences from Virginia Tech; Andrew H.
Knoll of Harvard, and the late J. John Sepkoski Jr. of the University of
Chicago, reports and analyzes evidence that only two of these mass
extinctions led to major change in global ecosystem structure. These were
the extinctions 251 million years ago, at the end of the Permian period,
and 65 million years ago, at the end of the Cretaceous period.
The Permian extinction was massive. It is believed to have wiped out 95
percent of all species, possibly as a result of increased levels of
dissolved CO2 in the oceans triggered by a comet or meteorite impact.
(Inclusions in Permian rocks containing gases known only to exist in outer
space were discovered only last year.) ...
However, the change in ecosystems was not produced by the killing events,
the article emphasizes, but by the way life evolved afterwards. "What we
think happened was that only these two big extinction events were severe
enough to so empty the world that the basic structure of the ecosystem
itself had to be re-established," says Bambach. "That took time, and as
things evolved, the pattern of ecologic relationship between different
adaptive types of organisms developed differently."