职称英语考试理工类阅读判断备考习题

职称英语考试理工类阅读判断备考习题

职称英语考试理工类阅读判断备考习题

新东方在线职称英语频道(http://www.360docs.net/doc/info-275b9416dd88d0d232d46a36.html /)分享职称英语考试理工类阅读判断备考习题

Lack of Oxygen Delayed the Rise of Animals on Earth

Scientists have long speculated as to why animal species didn’t flourish sooner, once sufficient oxygen covered the Earth’s surface. Animals began to prosper at the end of the Proterozoic period, about 800 million years ago — but what about the billion-year stretch before that, when most researchers think there also was plenty of oxygen?

Well, it seems the air wasn’t so great then, after all.

In a study published Oct. 31 in Science, Yale researcher Noah Planavsky and his colleagues found that oxygen levels during the “boring billion” period were only 0.1% of what they are today. In other words, Earth’s atmosphere couldn’t have supported a diversity of creatures, no matter what genetic advancements were poised to occur.

“There is no question that genetic and ecological innovation must ultimately be behind the rise of animals, but it is equally unavoidable that animals need a certain level of oxygen,” said Planavsky, co-lead author of the research along with Christopher Reinhard of the Georgia Institute of Technology. “We’re providing the first evidence that oxygen levels were low enough during this period to potentially prevent the rise of animals.”

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