在New York Times上看见这篇English报导没有明白

在New York Times上看见这篇English报导没有明白
氧浓度下的燃烧实验和动物灭绝的氧理论之间的矛盾,请你浏览下,
A Blow to the Oxygen Theory of Extinction
By KENNETH CHANG
Published:August 29,2008
Call it the clue of the moss that would not burn.It may show that a suspect in the largest mass extinction in Earth’s history is innocent after all.
For years,scientists have proposed various hypotheses for why about 90 percent of species living 250 million years ago suddenly died out.Some believe it was a meteor like the one that killed off the dinosaurs 135 million years later.Others have suggested massive volcanic eruptions or dropping ocean levels.
One idea that has attracted attention of late is that oxygen thinned precipitously,and animals died out simply because they did not have enough to breathe.But rocks of this era still contain charcoal,which means there was enough oxygen in the air for plants to burn.
So Claire Belcher,a biochemist at University College Dublin in Ireland,went into a room-size atmospheric chamber wearing an oxygen suit and spent a few months trying to burn things in low-oxygen air.Paper would not ignite at less than 14 percent oxygen,and even then,“It didn’t burn with a sustained flame,” Dr.Belcher said.
A candle would not ignite until oxygen reached a level of 17 percent by volume,and highly flammable pine wood did not burst into flames until oxygen reached 18 percent.Moss would not burn at all at less than 15 percent oxygen and did not really catch fire unless oxygen reached concentrations of 17 percent.Oxygen makes up 21 percent of present-day air.The results appear in the Aug.29 issue of the journal Science.
Dr.Belcher said the results did not rule out the oxygen hypothesis — the charcoal data is not detailed enough to detect an oxygen drop lasting just 100,000 years or so.But,she said,proponents of the idea need to look for more evidence in the rocks.