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 Beerling and his associates and on marine plankton growth at the University of Hawaii by a team led by Edward Laws and Brian Popp.

"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, W.P. Quick, 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 Hawaii.