首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
Lack of Oxygen Delayed the Rise of Animals on Earth Scientists have long speculated as to why animal species didn’t flourish
Lack of Oxygen Delayed the Rise of Animals on Earth Scientists have long speculated as to why animal species didn’t flourish
admin
2015-06-19
33
问题
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. "
The scientists found their evidence by analyzing chromium (Cr) isotopes in ancient sediments from China, Australia, Canada, and the United States. Chromium is found in the Earth’s continental crust, and chromium oxidation is directly linked to the presence of free oxygen in the atmosphere.
Specifically, the team studied samples deposited in shallow, iron-rich ocean areas, near the shore. They compared their data with other samples taken from younger locales known to have higher levels of oxygen.
Oxygen’s role in controlling the first appearance of animals has long vexed scientists. " We were missing the right approach until now," Planavsky said. "Chromium gave us the proxy. " Previous estimates put the oxygen level at 40% of today’s conditions during pre-animal times, leaving open the possibility that oxygen was already plentiful enough to support animal life.
In the new study, the researchers acknowledged that oxygen levels were "highly dynamic" in the early atmosphere, with the potential for occasional spikes. However, they said, "It seems clear that there is a first-order difference in the nature of Earth surface Cr cycling" before and after the rise of animals.
" If we are right, our results will really change how people view the origins of animals and other complex life, and their relationships to the co-evolving environment," said co-author Tim Lyons of the University of California-Riverside. "This could be a game changer. "
"There’s a lot of interest right now in a broader discussion surrounding the role that environmental, stability played in the evolution of complex life, and we think our results are a significant contribution to that," Reinhard said.
Tim Lyons liked to play computer games in his spare time.
选项
A、Right
B、Wrong
C、Not mentioned
答案
C
解析
题干说Tim Lyons空闲时间喜欢打电脑游戏。文章并没有提到该研究者的业余爱好,故故选C。
转载请注明原文地址:https://jikaoti.com/ti/eXysFFFM
本试题收录于:
职称英语理工类A级题库职称英语分类
0
职称英语理工类A级
职称英语
相关试题推荐
Poorchildrenshouldnotbedeprivedoftheopportunitytoparticipateinsportswheneverpossible.
EngineeringethicsisacompulsorysubjectineveryinstituteofscienceandtechnologyintheUnitedStates.Itislikelythat
EngineeringethicsisacompulsorysubjectineveryinstituteofscienceandtechnologyintheUnitedStates.Manyengineering
ManandComputerWhatmakespeopledifferentfromcomputerprograms?Whatisthemissingelementthatourtheoriesdon’tyet(51)
AnimalIntelligenceAreAnimalsintelligent?Iftheyare,whichanimalsarethemostintelligent?Thesearenoteasyquestionst
Practicallyallspeciesofanimalscommunicateeitherthroughsoundsorthroughalargerepertoryofsoundlesscodes.
ViennaViennawasoneofthemusiccentersofEuropeduringtheclassicalperiod,andHaydn,Mozart,andBeethovenwereall
Peopleknewlongagohowanearthquakestarts.Assoonasanearthquakeoccurs,studentsshouldleavethebuilding.
ArtificialSpeechBecausespeechisthemostconvenientformofcommunication,inthefuturewewantessentiallynaturalcon
随机试题
目前印度最著名的商业电视机构是()
感受器的刺激强度和被兴奋的纤维数目之间的关系是
细胞能主动吸收钠,排出钾,转运水,改变唾液的量和渗透压的是
Ⅱ度牙槽骨吸收指()
肾气虚不孕症的最佳治法是()
某客户2007年1月初购买了9万元A股票,若他计划在1年以后可以获得12万元,那么该客户要求的报酬至少为()。
请认真阅读下列材料,并按要求作答。请根据上述材料完成下列任务:设计本课板书。
业主委员会成立的条件不包括()。
下列地质景观与景区对应错误的是:
使用以下______命令可以启动菜单设计器对菜单进行修改。
最新回复
(
0
)