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
56
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.
The study revealed that chromium found in Earth’s continental crust remained stable before and after the rise of animals.
选项
A、Right
B、Wrong
C、Not mentioned
答案
B
解析
题干意思是,研究揭示,在陆地表面所发现的铬在动物大量繁殖前后是保持不变的。根据文章第八段“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.”可知,在动物大量繁殖前后,地球表面上铬的循环会出现差异。故本题故选B。
转载请注明原文地址:https://kaotiyun.com/show/sBGd777K
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
EngineeringethicsisacompulsorysubjectineveryinstituteofscienceandtechnologyintheUnitedStates.Severalengineeri
ManandComputerWhatmakespeopledifferentfromcomputerprograms?Whatisthemissingelementthatourtheoriesdon’tyet(51)
MysteriousNazcaDrawingsOneofthemostmysteriousarchaeologicalspectaclesintheworldistheimmensecomplexofgeome
GeorgiaO’Keeffe’sbest-knownpaintingsarethoseinwhichshemagnifiedflowersoranimalskullstofillthepicture.
Thestudyshowedthatmostofthegirls______.Whatkindofinstitutiondoestheleadresearcherworkwith?
Thestudyshowedthatmostofthegirls______.Thesurveyparticipantsweregirls______.
Theframeneedstobestrongenoughtosupporttheengine.
EnergyCycleDoyoufindgettingupinthemorningsodifficultthatit’spainful?Thismightbecalledlaziness,butDr.Kl
TakingaNapduringtheDayMedicalexpertssaymostAmericansdonotgetenoughsleep.TheysaymoreAmericansneedto【51】
随机试题
两审终审制意味着()
求极限
男性患者,14岁。以“进行性四肢无力3d,加重伴气急2h”来诊。查体,呼吸32/min,呼吸活动度差,脑神经正常,语音低微,四肢肌力1级,腱反射阴性,感觉系统未查及异常。测血钾3.8mmol/L,脑脊液:细胞数5×106/L,蛋白0.45g/L,糖3.
患者男性,30岁。主诉昨晚与朋友喝完酒在家休息3小时后,发现双下肢无力,很快上肢乃至全身无力,当时神志清楚,大小便不受影响。7小时后躯体、上肢逐渐恢复正常,下肢也明显好转,10小时后全部恢复正常;2周前曾发生相同症状1次。急诊化验血钾为2.5mmol/L。
肺炎喘嗽痰热闭肺证的用方是肺炎喘嗽心阳虚衰证的用方是
高尚医学道德对医学科学研究工作的重要意义,下列错误的是
根据我国土地管理法的规定,经()同意,报乡(镇)人民政府批准后,农民集体所有的土地可由本集体经济组织以外的单位或者个人承包经营。
具有质量轻、耐腐蚀、加工容易和施工方便等特点的非金属材料是()。
经营企业以加工贸易方式进出口的货物,不列人海关统计。()
2012年1—11月,我国软件产业总体保持平稳增长,实现软件业务收入2.19万亿元,同比增长27.3%,增速比1—10月提高1.5个百分点,比电子信息制造业高15个百分点,但低于去年同期5.5个百分点。其中11月完成收入2377亿元,同比增长41.4%,达
最新回复
(
0
)