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
64
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.
Many researchers believe the oxygen level was high during pre-animal times.
选项
A、Right
B、Wrong
C、Not mentioned
答案
A
解析
题干意思是许多研究者认为氧气的含量在史前动物时代是非常高的。根据文章第一段“…the billion-year stretch before that,when most researchers think there also was plenty of oxygen?”可知,大量研究者认为,在原生代之前的十亿年间,地球上存在着大量的氧气。而“pre-animal times"也就是“the end of the Proterozoic period”。
转载请注明原文地址:https://www.kaotiyun.com/show/IBGd777K
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
AAddressingaVarietyofBehavior-affectingFactorsBImportanceofImmunizationCRelationshipwithOtherHealthServicesD
ManandComputerWhatmakespeopledifferentfromcomputerprograms?Whatisthemissingelementthatourtheoriesdon’tyet(51)
Adeadlydiseasehasaffectedtheseanimals.
ASoot’sRoleinChangesintheClimateandtheAtmosphereBObservationsofWarmingintheNorthernHemisphereCExplanation
Peterisexperiencingadifficultperiodinhislife.
DevelopmentinNewspaperOrganizationOneofthemostimportantdevelopmentsinnewspaperorganizationduringthefirstpart
ArtificialSpeechBecausespeechisthemostconvenientformofcommunication,inthefuturewewantessentiallynaturalcon
HowtoSpentHisExtraTimeGiventhechoicebetweenspendinganeveningwithfriendsandtakingextratimeforhisschoolwo
TheSchoolCloseWhenschoolofficialsinKalkaska,Michigan,closedclasseslastweek,themediaflockedtothestory,port
随机试题
重症出血性水痘常发生在
患者,女,30岁,右肾结核,无功能,左肾轻度积水,功能尚可,膀胱容量正常,双上肺浸润性肺结核。目前的治疗措施是
急性泄泻取天枢、中脘是由于此二穴为
关于非法持有毒品罪,下列哪一选项是正确的?(2011—卷二—18,单)
某市位于经济技术开发区的甲醇合成厂房,厂区内设置多座储存甲醇的固定顶储罐,储罐直径45m。采用低倍数泡沫灭火系统进行保护。泡沫混合液的设计供给强度为10L/min·m2,连续供给时间30min,泡沫混合液的浓度为3%。经计算,罐内扑救一次火灾的泡沫混合液用
下列关于耕地占用税的说法正确的有()。
客户关系管理的核心是()。
格迪古城位于肯尼亚沿海地区中部马林迪市西南约15千米处,兴建于十二或十三世纪,逐渐发展成一个有3000人口左右的繁荣聚落,却在十六世纪末期突然消亡。虽然格迪古城的骤然废弃成为一桩________,学界对其原因迄今并无统一认识,但是格迪古城却相当_____
Formostaverageexercisersandathletes,sportsdrinksarenotonlyawasteofyourmoney,butmoreimportantly,canactuallyw
Anorganization’sreputation,profitability,andevenitscontinuedexistencecandependonthedegreetowhichitstargetedpub
最新回复
(
0
)