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
Why has life flourished on Earth? This question has a two-part, answer. First, Earth has been a cradle for life because of its p
Why has life flourished on Earth? This question has a two-part, answer. First, Earth has been a cradle for life because of its p
admin
2022-07-08
25
问题
Why has life flourished on Earth? This question has a two-part, answer. First, Earth has been a cradle for life because of its position relative to the Sun. Second, once life began on Earth, simple early life-forms (photosynthetic bacteria) slowly but inexorably altered the environment in a manner that not only maintained life but also paved the way for later, complex life-forms. These changes allowed later organisms to evolve and thrive. Humans and other higher organisms owe their life-supporting environment to these early life-forms.
Earth’s earliest atmosphere contained several gases: hydrogen, water vapor, ammonia, nitrogen, methane, and carbon dioxide, but no oxygen. Gas mixtures
emitted
from present-day volcanoes resemble this early atmosphere, suggesting its origin from volcanic eruptions. In Earth’s earliest atmosphere, methane and carbon dioxide occurred at much higher levels than at present—a circumstance that was favorable for early life. Methane and carbon dioxide are greenhouse gases that warm atmospheres by
retarding
loss of heat to space. These two gases kept Earth warm during the Sun’s early history, when the Sun did not bum as brightly as it now does. (An early dim period, with later brightening, is normal for stars of our Sun’s type.)
Earth’s modern atmosphere, which is 78 percent nitrogen gas, 21 percent oxygen, and about 1 percent argon, water vapor, ozone, and carbon dioxide, differs dramatically from the earliest atmosphere just described. The modern atmosphere supports many forms of complex life that would not have been able to exist in Earth’s first atmosphere because the oxygen level was too low. Also, if atmospheric methane and carbon dioxide were as abundant now as they were in Earth’s earliest atmosphere, the planet’s temperature would likely be too hot for most species living today. How and when did the atmosphere change?
The answer to this riddle lies in the metabolic activity of early photosynthetic life-forms that slowly but surely transformed the chemical composition of Earth’s atmosphere. Some of these early organisms were photosynthetic relatives of modem cyanobacteria (blue-green bacteria). In the process of photosynthesis, carbon dioxide gas combined with water yields oxygen. In Earth’s early days, all over the planet countless photosynthetic bacteria performed photosynthesis. Together, these ancient bacteria removed massive amounts of carbon dioxide from Earth’s atmosphere by converting it to solid organic carbon. These ancient bacteria also released huge quantities of oxygen into the atmosphere. Other ancient bacteria consumed methane, greatly reducing its amount in the atmosphere. When our Sun later became hotter, the continued removal of atmospheric carbon dioxide and methane by early bacteria kept Earth’s climate from becoming too hot to
sustain
life. Modern cyanobacteria still provide these valuable services today.
The word sustain in the last paragraph is closest in meaning to________.
选项
A、change
B、generate
C、destroy
D、support
答案
D
解析
本题为词义题。sustain意为“维持,支持”,在文中最后一段倒数第2句指“维持地球生命的存活”,因此D项“支持,支撑”与之意思最为接近,符合要求。A项“改变”、B项“产生,生成”、C项“破坏”,均不符合要求。
转载请注明原文地址:https://kaotiyun.com/show/zs0O777K
本试题收录于:
CATTI二级笔译综合能力题库翻译专业资格(CATTI)分类
0
CATTI二级笔译综合能力
翻译专业资格(CATTI)
相关试题推荐
Whichoneisdeemedas"lesshealthy"inLondonbyPublicHealthEngland?
Willmeditationongoodthoughtsleadtoabetterworld?
Humanshavealwayslookedattheheavensand【C1】______aboutthenatureoftheobjectsseeninthenightsky.Withthedevelopmen
Ireadsomeofmypoetryaloudtothem,butitwascastingpearlsbeforeswine.Theyobviouslydidn’tunderstandawordofitan
Inthepastfewyears,I’vetaughtnonfictionwritingtoundergraduatesandgraduatestudentsatHarvard,Yale,andColumbia’sS
Beforeoureyes,theworldisundergoingamassivedemographictransformation.Globally,thenumberofpeopleage60andoveris
"Thelanguageofacomposer",Carduswrote,"hisharmonies,rhythms,melodies,colorsandtexture,cannotbeseparatedexceptby
Itseemsoilleavesfromthispipeforsometime.We’llhavetotakethemachineaparttoputitright.
"Yourealizethatyouweredrivingat100mph,don’tyou?""No,officer,Imaynothavebeen.Thiscarcan’tdomorethan80."
Researchersallovertheworldhavebeenseekingfordetermininghowearlyinfancyconceptualthinkingispossible.
随机试题
收集胃、肠、脾、胰血液回流的静脉血管是()
在搅拌水泥混温土混合料时,宜按()的顺序投料。
水利工程建设发生重大质量与安全事故后,必须迅速,有效地实施先期处置,防止事故进一步扩大的单位是()。
输入期初余额时,上级科目的余额和累计发生数据需要手工输入。()
财产保险属于客户可能提出的其他要求中的哪项?()。
甲公司为房地产开发企业,2×20年发生有关房地产投资的资料如下:(1)1月1日购入一块土地,并开始在其上建造一栋用于对外出租的写字楼,购入当日董事会即作出完工后对外出租的书面决议,但尚未签订租赁合同。该项土地购买价款为1200万元。为购建写字楼占用了2
根据助人自助的理念,在某个家庭面临贫困时,社会工作者的服务内容包括()。
讲授法意味着灌输式教学。
油价上涨给社会生产和人民生活造成影响。你认为应如何应对?
()对于严寒相当于军队对于()
最新回复
(
0
)