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2015年全国职称英语考试于3月28日(9：00-11：00)举行。针对考后考生最关注的2015职称英语考试真题及答案解析问题，英语网在考后第一时间为您整理发布2015职称英语考试真题及答案解析：理工类。预祝各位考生顺利通过2015职称英语考试! Lackof Oxygen Delayed the Rise of Animals on Earth Scientistshave long speculated as to why animal species didnt flourish sooner,oncesufficient oxygen covered the Earths surface.Animals began to prosper at theend of the Proterozoic period,about 800 million years agobut what about thebillion-year stretch before that,when most researchers think there also wasplenty of oxygen？ Well,it seems the air wasnt so great then,after all. Ina study published Oct.31 in Science,Yale researcher Noah Planavsky and hiscolleagues found that oxygen levels during the boring billionperiod wereonly 0.1% of what they are today.In other words,Earths atmosphere couldnthave supported a diversity of creatures,no matter what genetic advancementswere poised to occur. There is no questionthat genetic and ecological innovation must ultimately be behind the rise ofanimals,but it is equally unavoidable that animals need a certain level ofoxygen,said Planavsky,co-lead author of the research along with ChristopherReinhard of the Georgia Institute of Technology.Were providing the firstevidence that oxygen levels were low enough during this period to potentiallyprevent the rise of animals. | 
