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One Study Contradicts Another On Oxygen Content Of Dinosaurs’ Air

December 8, 1987

SAN FRANCISCO (AP) _ A study of gas bubbles trapped in fossilized tree resin contradicts previous research suggesting the modern atmosphere contains only two-thirds as much oxygen as it did when dinosaurs roamed the planet.

The author of the earlier study, Yale University geochemist Robert Berner, insisted his findings were correct in indicating Earth’s air 80 million years ago contained 32 percent oxygen, compared with 21 percent today.

Berner and Scripps Institution of Oceanography geologist Harmon Craig both measured the gas content of bubbles trapped in amber, fossilized resin from ancient trees, a substance that is different from watery tree sap.

However, when Craig and Scripps chemist Yoshio Horibe crushed 80-million- year -old Canadian amber, they found it contained no oxygen, a direct contradition of Berner’s findings, Craig said Monday during the American Geophysical Union’s fall meeting.

Each scientist said the other’s research was faulty.

The initial study by Berner and U.S. Geological Survey scientist Gary Landis was widely publicized when it was presented last October during a geology convention in Phoenix, Ariz. They found 80-million-year-old amber from Canada contained bubbles with up to 32 percent oxygen, while 40-million-year- old amber from the Baltic Sea region contained 21 percent oxygen, the same level in modern air.

The Berner-Landis study was significant because it purportedly was the first direct look at Earth’s atmosphere during the era of the dinosaurs, and because scientists had always thought the atmosphere then had about the same makeup as it does today.

Some scientists also said a drop in atmospheric oxygen might explain why the dinosaurs became extinct 65 million years ago, an alternative to the controversial theory that asteroid collisions with Earth kicked up so much dust that sunlight was blocked, wiping out the dinosaurs’ food supply.

Craig said he believes the oxygen in the amber Berner and Landis studied really came from water that was taken up by tree roots, not from air. That is because the the ratio of nitrogen gas to argon gas in the amber suggests those gases also originated in water, he added.

During a telephone interview from New Haven, Conn., Berner expressed irritation with Craig’s criticism, saying the method he and Landis used to measure gases trapped in amber was much more sensitive than the technqiue used by Craig and Horibe.

Berner said he and Landis first broke chunks of amber into slightly smaller pieces, freeing and analyzing the gas contained in relatively large bubbles in 80-million-year-old amber. The bubbles contained 32 percent oxygen, he added.

Berner said Craig and Horibe simply crushed the amber into fine particles, liberating other gases that either were trapped in very tiny air bubbles or dissolved in the amber itself.

Those gases contain no oxygen, just as Craig and Horibe found, Berner said. Because non-oxygen gases make up most of the gases in the amber, Craig and Horibe simply couldn’t detect the small amount of oxygen-rich air trapped in larger bubbles, he added.

Since the Phoenix meeting, Berner said he and Landis analyzed air from bubbles trapped in 80-million-year-old amber from New Jersey, and found it also contained up to 32 percent oxygen.

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