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
THREE THEORIES ABOUT ORIGIN OF LIFE (1) Oxygen and nitrogen are major components of our current atmosphere. But the kinds of
THREE THEORIES ABOUT ORIGIN OF LIFE (1) Oxygen and nitrogen are major components of our current atmosphere. But the kinds of
admin
2022-09-29
60
问题
THREE THEORIES ABOUT ORIGIN OF LIFE
(1) Oxygen and nitrogen are major components of our current atmosphere. But the kinds of hydrogen reactions with other gases that are required to transform simple organic molecules into complex ones are interrupted by oxygen, which combines with hydrogen atoms from other compounds. Therefore, life on Earth must have originated when there was very little oxygen in Earth’s atmosphere. The modern scientific theory of life’s origin was first formulated in the 1920s by Russian scientist Aleksandr Oparin and independently by British scientist J. B. S. Haldane. The assumption that life sprang up from chemical reactions that were initiated in the early atmosphere (oxygen-poor/hydrogen-rich) and came to completion in the early oceans was posited by the Oparin-Haldane hypothesis, as it came to be called. Oparin and Haldane suggested that the hydrogen-containing gases were caused to react with each other to form organic compounds by energy sources such as sunlight and lightning.
(2) With regard to the view that these complex organic compounds could have begun to shape in Earth’s oceans, some researchers remain
skeptical
. The probability that the fundamental building blocks of life, formaldehyde (CH
2
O) and hydrogen cyanide (HCN), even though they were probably available, would have been concentrated sufficiently to allow further reactions to occur was likely small. And the more complex organic compounds that might have formed in this way would not have lasted long in the surface of the ocean environment, because photochemical and thermal reactions would have destroyed them. Therefore, researchers have sought alternative explanations for how complex organic compounds formed.
(3) There is one possibility that the relevant organic compounds were created in space, and asteroids or comets brought them to Earth, probably as tiny dust particles. Recovered from the stratosphere (an upper region of Earth’s atmosphere), interplanetary dust particles (IDPs) are tiny particles that are known to be extraterrestrial origin. From research, we know that organic compounds, including amino acids, exist in IDPs as well as in some meteorites. It is believed that they form from reactions between charged particles and neutral molecules. Those atoms appear in interstellar dust clouds at very low temperatures—on the order of 200 or more degrees below zero on the Celsius scale.
It may seem surprising that organic chemistry could occur in the interstellar environment, but it. is precisely the extremely low temperatures involved that allow complex organic molecules to exist because temperatures are too cold to allow them to decompose.
(4) [A] It is thought that some of the molecules created in the interstellar environment have survived the collapse of the gas and dust cloud that formed our solar nebula and Sun. [BJ They would have been incorporated into solid materials that condensed out of the nebula and formed asteroids and comets. [C] Such materials might have been delivered to Earth in great quantities during the heavy bombardment period of solar system history, between 4.5 and 3.8 billion years ago. [D]
(5) The hypothesis that life took place in or around hydrothermal vents (hot springs), where new seafloor is being created along mid-ocean ridges (underwater mountain chains) at the ocean’s bottom is the third theory of life’s origin. Seawater that flows a kilometer or more down through crevices in the rock, is heated, and then rises rapidly back to the surface, and the ridges are cooled. During the process, the water gathers substances such as hydrogen, hydrogen sulfide, and dissolved ferrous iron. When it meets the cold water, the extremely hot (350 degree centigrade) vent water generates a dark plume comprised mostly of iron sulfide, a compound produced by the reaction between ferrous iron and hydrogen sulfide.
(6)Still, the explanation that submarine hydrothermal vents are a likely place for life to have originated is controversial. In vent systems, there are various types of materials from which organic molecules can be synthesized. However, complex organic molecules are not stable at the high temperatures observed in vents positioned directly on the axis of a ridge. If life did originate at the mid-ocean ridges, it probably did so in cooler, off-axis vents. Some researchers claim that the perfect place for life to have begun would be in some near-freezing surface environment because even the off-axis vents are too warm. The dispute as to whether life originated in a hot or cold environment is unlikely to stop.
The word "skeptical" in the paragraph 2 is closest in meaning to ________.
选项
A、doubtful
B、confident
C、hopeful
D、puzzled
答案
A
解析
本题属于词汇题,考查考生对skeptical的理解。skeptical意为“怀疑的”,A项doubtful同样意为“怀疑的”,是skeptical的同义词,故选。B项confident“自信的”、C项hopeful“抱有希望的”和D项puzzled“困惑的”均未能体现skeptical的意思。
转载请注明原文地址:https://www.kaotiyun.com/show/3s5O777K
0
托福(TOEFL)
相关试题推荐
WriteNOMORETHANTWOWORDSAND/ORANUMBERforeachanswer.MonarchButterfliesHibernationButterflyspeciesadoptdifferent
7am——3pm本题有关该工作的工作时间。录音原文中的from…includingsomeweekends…eveningshifts是题目的同义替换。
TheTawnyOwlMost【L31】________owlspeciesinUKStronglynocturnalHabitatMainlylivesin【L32】________,butcanalsobeseeni
TheTawnyOwlMost【L31】________owlspeciesinUKStronglynocturnalHabitatMainlylivesin【L32】________,butcanalsobeseeni
ChooseTWOletters,A-E.WhichTWObusinessfacilitiesarementioned?AinternetaccessBmobilephonehireCaudio-visua
AustralianAboriginalArtAncientartrockandbarkpaintingsanddrawings【L31】______________decorationso
CITYARCHIVESAnineteenth-centurydocumentsBmapsCpersonalpapersDphotographsEbooksaboutthecityFnewspapersGin
WelcometoCityArchivesThefollowingpeoplemayusethearchives:Universitystudentswithavalid【L21】________Cityresidents
A、Shewillgototherestaurantwiththeman.B、Shewillmeetthemanandhisfriendslaterintheevening.C、Shehasalreadyha
TheEUmeetingcomesadayafterPresidentNicolasSarkozyofFrance,whichholdstherotatingEUpresidency,securedagreement
随机试题
提高冒口补缩效率的途径说法错误的是()。
《合同法》第120条规定:“当事人双方都违反合同的,应当各自承担相应的责任。”双方违约应发生在________,但不限于双务合同。
ACTH是指:()
关于慢性粒细胞白血病(慢性期)血象的叙述,错误的是
某施工企业拥有一处办公楼,评估价为6000万元。该施工企业从A银行贷款4000万元,从B银行贷款2000万元,并与B银行办理了抵押登记。后该施工企业无力还款,经诉讼后拍卖办公楼,取得售楼款5000万元用于清偿A、B银行债务。A、B银行债权的分配数额应为(
乙公司以一项债权换入一项短期投资,支付的补价为50万元。换出债权的账面余额为200万元,计提的坏账准备为20万元。换入的短期投资中包括已宣告发放但尚未领取的现金股利30万元。假定不考虑相关税费,甲公司换入的该项短期投资的入账价值为()万元。
维护统治秩序与惩罚犯罪的客观需要,是警察产生的社会条件。()
根据以下资料,回答下列问题。2012年末,中国大陆总人口135404万人,全年出生人口1635万人,死亡人口966万人。从性别结构看,男性人口69395万人,同比增加327万人,女性人口66009万人,同比增加342万人;从城乡结构看,城镇人口7
以下关于"查询"的正确描述是( )。
相对于数据库系统,文件系统的主要缺陷有数据关联差、数据不一致性和()。
最新回复
(
0
)