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 ago but 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.
Thescientists found their evidence by analyzing chromium (Cr) isotopes in ancientsediments from China,Australia,Canada,and the United States.Chromium isfound in the Earths continental crust,and chromium oxidation is directlylinked to the presence of free oxygen in the atmosphere.
Specifically,the team studied samples deposited in shallow,iron-rich ocean areas,near theshore.They compared their data with other samples taken from younger localesknown to have higher levels of oxygen.
Oxygensrole in controlling the first appearance of animals has long vexed scientists.We were missing the right approach until now,Planavsky said.Chromium gaveus the proxy.Previous estimates put the oxygen level at 40% of todaysconditions during pre-animal times,leaving open the possibility that oxygenwas already plentiful enough to support animal life.
Inthe new study,the researchers acknowledged that oxygen levels were highlydynamicin the early atmosphere,with the potential for occasional spikes.However,they said,It seems clear that there is a first-order difference inthe nature of Earth surface Cr cyclingbefore and after the rise of animals.
If we are right,ourresults will really change how people view the origins of animals and othercomplex life,and their relationships to the co-evolving environment,saidco-author Tim Lyons of the University of California-Riverside.This could be agame changer.
Fundingsources for the research included the NASA Exobiology Program and the NationalScience Foundations Earth-Life Transitions program,awarded to Planavsky,Reinhard,and Lyons.
Theother members of the research team included Xiangli Wang,a postdoctoral fellowat Yale; Thomas Johnson,of the University of Illinois; Danielle Thomson,ofCarleton University; Peter McGoldrick,of the University of Tasmania; andWoodward Fischer,of the California Institute of Technology.
16.The study discovered the rise of animals occurred earlier than the Proterozoicperiod.
A.Right B.Wrong C.Not mentioned
17.Many researchers believe the oxygen level was high during pre-animal times.
A.Right B.Wrong C.Not mentioned
18.The teamwas funded by several research institutes.
A.Right B.Wrong C.Not mentioned
19.Geneticadvancements triggered the rise of animals.
A.Right B.Wrong C.Not mentioned
20.Thesamples studied in the research were collected in ocean areas.
A.Right B.Wrong C.Not mentioned
21.Thestudy revealed that chromium found in Earths continental crust remained stablebefore and after the rise of animals.
A.Right B.Wrong C.Not mentioned
22.TimLyons liked to play computer games in his spare time.
A.Right B.Wrong C.Not mentioned
深度剖析A类雅思阅读判断题
详解雅思阅读被动语态的几种特殊用法
雅思阅读技巧:定义式线索猜测法
名师教你如何分析雅思阅读文章的脉络
中国考生做雅思阅读T/F/NG题的五大误区
雅思阅读判断题的审题及解题思路
雅思阅读段落细节信息配对题的攻克方法
第一次做雅思阅读的四大问题总结
雅思阅读基础学习的障碍:词汇习得
雅思阅读难点因素之一:英语词汇
雅思阅读备考应做好精读泛读的结合
雅思阅读快速提分首先要攻克单词和句子关
雅思阅读分词难句结构分析
助攻雅思阅读高分的硬件与软件
雅思阅读背景词汇:天文学之八大行星
雅思阅读备考最常见的7个问题及其克服办法
雅思阅读背景知识:ambergris 龙涎香
雅思阅读背景知识:大脑风暴
雅思阅读T/F/NG是隔句读还是快速浏览
考前三天的雅思阅读备考注意事项
雅思阅读段落标题配对题的6个题型特点
雅思阅读文章不需详读 只需做到3个S
雅思阅读文章脉络的把握方法
雅思阅读背景知识:香蕉的进化
雅思阅读Summary completion题型的应对策略
雅思阅读练习的首位要素是时间
雅思阅读全部倒装的几种情况分析
五步轻松搞定雅思阅读信息段落配对题
浅谈雅思阅读是非题的显性考点原则
雅思阅读9分需弄清读题与看文章的顺序
不限 |
英语教案 |
英语课件 |
英语试题 |
不限 |
不限 |
上册 |
下册 |
不限 |