Science/Medicine : Oxygen Study Disputed

A widely publicized study showing the oxygen content of Earth’s atmosphere has dropped sharply since the era of the dinosaurs has been disputed by a scientist who measured air bubbles trapped in fossilized tree resin.

But the author of the original study, Yale University geochemist Robert Berner, insisted his findings are correct in showing Earth’s air 80 million years ago contained 32% oxygen, compared with 21% today.

Both Berner and Scripps Institution of Oceanography geologist Harmon Craig, who presented his contradictory study last week at the American Geophysical Union’s fall meeting, measured the gas content of bubbles trapped in amber, which is fossilized resin from ancient trees.

The initial study by Berner and U.S. Geological Survey scientist Gary Landis found 80-million-year-old amber contained bubbles with up to 32% oxygen, while 40-million-year-old amber contained 21% oxygen, the same level in modern air.

But Harmon said that when he and Scripps chemist Yoshio Horibe crushed 80-million-year-old amber, they found it contained no oxygen. Further, the ratio of nitrogen gas to argon gas in the amber suggests those gases had been dissolved in water in tree sap.