Thursday, December 5, 1996
RESEARCH:
Study results in unique, statistical extinction explanationBy
Teresa Jun
Daily Bruin Contributor
For many people, news concerning the extinction of dinosaurs may
seem as old as dinosaur fossils themselves. But those who study the
field know that the question of what exactly caused the extinction
65 million years ago is still hotly debated among scientists
today.
For Earth and Space Sciences Associate Professor Charles R.
Marshall, this debate has finally progressed toward a resolution.
In a new study co-authored with Geology Professor Peter Ward of the
University of Washington, Marshall provides an innovative
statistical explanation for the extinction of dinosaurs and other
species.
Recently, the Science journal published the results of their
research in a front cover story.
The classic extinction debate centers around what exactly caused
the mass extinction of most species world-wide 65 million years
ago. Ward and Marshall’s study presents evidence that while more
than one factor caused the extinctions, a meteorite impact was
responsible for the majority of the mass extinction.
"Some scientists claim that a huge meteorite struck the earth
during this time and caused a sudden extinction," said Professor
Marshall. "Others say that the impact was nothing. They say that
the fossil record shows a pattern of natural extinctions with
species gradually tapering off long before the impact."
According to Marshall, the problem with the on-going dispute is
that the fossil record is too incomplete to draw conclusions from
it by observing the record literally.
"Imagine that a woman dies," he explains. "And the only record
of her existence that she leaves behind is her checkbook. Now, how
would you go about determining what day she died?" Simply looking
at the date of the last check she wrote would not be helpful
because that may not necessarily be the day that she died,
according to Marshall, who said a more accurate approach would be
to observe the pattern of her previous check-writing.
"We wouldn’t be able to precisely pinpoint the exact date," said
Marshall. "But by observing the frequency of the checks, a span of
time in which she died can be somewhat accurately determined. This
margin of error is the same approach we must take with all of our
available fossil data."
Marshall uses this analogy to clarify the unconventional
approach he took in this research, which has been commended by his
colleagues in the field.
"This study statistically proves that the last time you see a
fossil of a particular species is not necessarily the last time the
species existed," supported Frank Kyte, researcher and geochemist
in the Institute of Geophysics and Planetary Physics.
By applying a statistical analysis to the well-documented fossil
record collected by Ward, Marshall’s analysis avoids the
shortcomings of previous scientific explanations. Two common
shortcomings are reliance on either a literal interpretation of the
fossil data or a broad "guesstimate" approach to the fossil
record.
The conclusions of the study indicate that a combination of
factors contributed to the mass extinctions. According to the
study, about 50 percent of the extinctions were caused by the
impact of the meteorite  a surprising statistic for
scientists at both extremes of the debate. Another 25 percent
became extinct due to a substantial drop in sea level, and the
remaining 25 percent became extinct through "background
extinction," extinctions that would have occurred naturally with
time.
"Ward’s and Marshall’s research is the first really proper
analysis of what happened at the end of the Cretaceous," commented
Earth and Space Sciences Department Chairman Bruce Runnegar. "They
apply a thorough, mathematical analysis to the imperfect,
incomplete fossil record."
Their thorough analysis was the result of years of hard work in
the field. Ward had been accumulating a rich fossil data set for
several years before Professor Marshall approached him with his
hypothesis.
"I kept myself updated with his records. His data sets were a
classic in the field," Marshall recalled. "I wanted to test my
hypothesis by applying it to his exceptional fossil record."
As a result of this cooperative union, Marshall and Ward spent a
week in the south of France, analyzing fossil deposits during the
summer of 1994.
Their days were spent doing field work in the rich fossil
deposits of the northern coast of Spain, near the French
border.
One of the photographs taken of the fossil site during this
expedition was chosen by the Science committee to appear on the
front cover of the magazine.
This past summer, when Marshall found out that the research
article he and Ward had submitted to Science was accepted for
print, he said he was very excited, since it was the first time
that he had ever submitted anything to Science for publication.
Several weeks later, when the journal committee announced its
decision to print his photo on the front cover and promote his
article to a cover story, "Cool!" was his initial, giddy
reaction.
The next step for Marshall in this research is to create
statistical models and conduct further critical analyses of the
extinction. But for the most part, the toughest part is over for
the UCLA professor of six years.
"Scientists will never all agree about what really caused the
extinction," added Kyte. "But Professor Marshall’s study provides
an important statistical tool to go about analyzing the imperfect
fossil record."
JUSTIN WARREN/Daily Bruin
Charles Marshall, Associate Professor-Earth & Space
Sciences, conducts research which focuses on a more statistical
explanation for the cause of dinosaur and other species
extinction.