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Extinctions



[ I probably ought to do this in a separate message... maybe I'll do it
  again when I get around to modifying the moderation rules.  I've
  decided to cover my bum as much as possible with respect to
  copyright protections, so I will no longer distribute messages which
  contain newspaper articles and such things even if they were
  delivered to you electronically.  If you'd like to draw our
  attention to such things, either summarize them, tell us where to
  find them, or get advance permission to redistribute them.
  Otherwise they're not going to get past me.  The following is a
  press release, so I'm presuming that it is meant to be distributed
  far and wide without the fear of stepping on anyones' copyrights.
  If you think I'm wrong about that, please let me know.  -- MR ]

Thought the list may be interested in the following from the National 
Science Foundation.

Media contact:                                November 21, 1996
Cheryl Dybas                                       NSF PR 96-75
(703) 306-1070

Program contact:
Chris Maples
(703) 306-1551

IMPACT OF METEORITE, DROP IN SEA LEVEL CAUSED MASS EXTINCTIONS
                        65 MILLION YEARS AGO

     The scientific dispute over what caused the extinction of
70 percent of all species worldwide 65 million years ago is
closer to a resolution, with new research by scientists from
UCLA and the University of Washington.  The research was funded
by the National Science Foundation (NSF).

     A cover story in the November 22 issue of the journal
Science reports the researchers' evidence supporting the
controversial theory that the extinction of dinosaurs and many
other species was caused by the impact of a huge meteorite that
crashed to Earth some 65 million years ago.

     "The end-Cretaceous extinction is one of the largest mass
extinctions in Earth's history, and its cause has been among
the most contentious, hotly debated issues in paleontology,"
says Chris Maples, program director in NSF's division of earth
sciences.  "This work by Marshall and Ward is important because
it may result in more agreement among proponents of different
end-Cretaceous extinction scenarios."

     However, the scientists -- paleontologist Charles Marshall
of UCLA and geologist Peter Ward of the University of
Washington in Seattle -- also present evidence that other
factors, including a drop in sea level prior to the assault by
the massive asteroid or comet, also may have caused some of the
extinctions at the end of what is known as the Cretaceous
period.  Marshall and Ward present evidence demonstrating that
a combination of factors caused the mass extinctions.

     Marshall applied statistical analysis to a well-preserved
and well-documented fossil record which Ward has collected -
some 40 species of sea creatures from the Cretaceous period
that include clams and squid-like creatures with shells called
ammonites.

     "For the first time, we can estimate the relative
importance of all the major factors that led to the extinction
of the ammonites," says Marshall.  The impact of the asteroid
or comet accounts for 50 to 75 percent of the ammonite
extinctions, which is a much higher figure than some scientists
had expected, but lower than others anticipated, he says.  The
substantial drop in sea level, which had peaked at least 10,000
years before the comet struck, accounts for between zero and 25
percent of the extinctions.  In addition, about 25 percent of
the extinctions were due to factors that would have occurred
regardless of the meteorite or the change in sea level -- what
scientists call "background extinction."

     "Some scientists thought the extinctions were due solely
to the impact of the asteroid or comet, others thought they
were due to the sea level change, and still others thought that
background extinction accounted for most of the extinctions;
we're seeing evidence that all of them were factors," says
Marshall.

     Marshall and Ward found evidence for a decline in the
abundance of species, and perhaps the extinction of more
species than would have occurred normally, during the time sea
level dropped substantially.  In addition, the scientists found
that there was a mass extinction of species most likely caused
by the impact of the asteroid or comet.

                             -NSF-
*****************************************************************
Janet E. Benoit                                 jebenoit@nidc.edu