CONTACT: Karen Peart 203-432-1326 #207

New Haven, Conn.. — A new method of calculating oxygen in the
Earth’s atmosphere suggests that an increase more than 300 million years
ago was caused by the rise and spread of trees and other vascular land
plants, a Yale study finds.

The new plant life produced dead organic matter resistant to decomposition
by bacteria that was buried in sediments, and, as a result, extra oxygen
was added to the atmosphere by increased global photosynthesis, according
to Robert A. Berner, the Alan M. Bateman Professor of Geology and Geophysics at Yale.

“The rise of large vascular land plants had a significant effect on
atmospheric composition, both oxygen and carbon dioxide,” said Berner.

The higher concentrations of oxygen lasted for 100 million years and were
significantly higher than the Earth’s current oxygen content of 21
percent. Published in the March 3 issue of Science, the study shows that
the calculated high oxygen levels during this period verify earlier
independent estimates and that this high oxygen may have been an important
factor in affecting the evolution of giant insects.

The study’s theoretical calculations rest partly on experimental work on
land plant growth at the University of Sheffield in England by David
and his associates and on marine plankton growth at the
University of Hawaii by a team led by Edward Laws and Brian

“As a result of these experiments, we were better able to calculate
realistic changes in atmospheric oxygen over geologic time,” Berner said.

In addition to Berner, Beerling, Laws and Popp, the study’s team included
former Yale graduate student, Steven T. Petsch, and J. A. Lake,
, and F.I. Woodward from the University of Sheffield in
England; and
R.S. Lane, M.B. Westley
and N. Cassar from the University of

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