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
"Life in Our Solar System" Although we can imagine life based on something other than carbon chemistry, we know of no example
"Life in Our Solar System" Although we can imagine life based on something other than carbon chemistry, we know of no example
admin
2018-07-24
31
问题
"Life in Our Solar System"
Although we can imagine life based on something other than carbon chemistry, we know of no examples to tell us how such life might arise and survive. We must limit our discussion to life as we know it and the conditions it requires. The most important requirement is the presence of liquid water, not only as part of the chemical reactions of life, but also as a medium to transport nutrients and wastes within the organism.
The water requirement automatically eliminates many worlds in our solar system. The moon is airless, and although some data suggest ice frozen in the soil at its poles, it has never had liquid water on its surface. In the vacuum of the lunar surface, liquid water would boil away rapidly. Mercury too is airless and cannot have had liquid water on its surface for long periods of time. Venus has some traces of water vapor in its atmosphere, but it is much too hot for liquid water to survive. If there were any lakes or oceans of water on its surface when it was young, they must have evaporated quickly. Even if life began there, no traces would be left now.
The inner solar system seems too hot, and the outer solar system seems too cold. The Jovian planets have deep atmospheres, and at a certain level, they have moderate temperatures where water might condense into liquid droplets. But it seems unlikely that life could begin there. The Jovian planets have no surfaces where oceans could nurture the beginning of life, and currents in the atmosphere seem destined to circulate gas and water droplets from regions of moderate temperature to other levels that are much too hot or too cold for life to survive.
A few of the satellites of the Jovian planets might have suitable conditions for life. Jupiter’s moon Europa seems to have a liquid-water ocean below its icy crust, and minerals dissolved in that water would provide a rich broth of possibilities for chemical evolution. A Nevertheless, Europa is not a promising site to search for life because conditions may not have remained stable for the billions of years needed for life to evolve beyond the microscopic stage. B If Jupiter’s moons interact gravitationally and modify their orbits, Europa may have been frozen solid at some points in history. C
Saturn’s moon Titan has an atmosphere of nitrogen, argon, and methane and may have oceans of liquid methane and ethane on its surface. D The chemistry of life that might crawl or swim on such a world is unknown, but life there may be unlikely because of the temperature. The surface of Titan is a deadly -179°C (-290°F). Chemical reactions occur slowly or not at all at such low temperatures, so the chemical evolution needed to begin life may never have occurred on Titan.
Mars is the most likely place for life in our solar system. The evidence, however, is not encouraging. Meteorite ALH84001 was found on the Antarctic ice in 1984. It was probably part of debris ejected into space by a large impact on Mars. ALH84001 is important because a team of scientists studied it and announced in 1996 that it contained chemical and physical traces of ancient life on Mars.
Scientists were excited too, but being professionally skeptical, they began testing the results immediately. In many cases, the results did not confirm the conclusion that life once existed on Mars. Some chemical contamination from water on Earth has occurred, and some chemicals in the meteorite may have originated without the presence of life. The physical features that look like fossil bacteria may be mineral formations in the rock.
Spacecraft now visiting Mars may help us understand the past history of water there and paint a more detailed picture of present conditions. Nevertheless, conclusive evidence may have to wait until a geologist in a space suit can wander the dry streambeds of Mars cracking open rocks and searching for fossils.
We are left to conclude that, so far as we know, our solar system is bare of life except for Earth. Consequently, our search for life in the universe takes us to other planetary systems.
Why does the author mention the meteorite "ALH84001" in paragraph 6?
选项
A、Because it was found in Antarctica about fifty years ago
B、Because it was evidence of a recent impact on Mars
C、Because scientists thought that it contained evidence of life on Mars
D、Because the meteorite probably came from Mars a long time ago
答案
C
解析
"ALH84001 is important because a team of scientists studied it and announced in 1996 that it contained chemical and physical traces of ancient life on Mars." Choice A is not correct because the meteorite was found closer to twenty years ago. Choice B is not correct because the impact on Mars was not recent. Choice D is true, but it is not the reason why the author mentions the meteorite.
转载请注明原文地址:https://kaotiyun.com/show/ZkfO777K
0
托福(TOEFL)
相关试题推荐
Completethenotesbelow.WriteONEWORDONLYforeachanswer.NotesonCustomer’sInformationExampleAnswerInforma
Choosethecorrectletter,A,BorC.The"ReturningStudentsAdvisor"ConsultationWhatdoesthemanwanttohave?
Choosethecorrectletter,A,BorC.Themethodofdatacollectionwas
Completethenotesbelow.WriteNOMORETHANTHREEWORDSforeachanswer.GIVINGASPEECHReasonsfornervousnessLecturers
Choosethecorrectletter,A,BorC.Whoisthetargetaudience?
ChooseTWOletters,A-E.WhichTWObenefitsofthisactivitytothestudentsarementionedbytheprofessor?ATheybecomemore
AccordingtoBetty,whatcanbesaidaboutthesalesofbothcheeseandoilinNewZealandandColombia?
Whichadvantageismentionedforeachofthefollowingrestaurants?ChooseSIXanswersfromtheboxandwritethecorrectletter
Choosethecorrectletter,A,BorC.WhatdoestheprofessoradviseDouglastodoabouttheformationofthefocusgroups?
Whichofthefollowingareexamplesofthemarketingfunctionofharvesting?Clickontwoanswers.
随机试题
A.威灵仙B.防己C.狗脊D.独活E.木瓜既能祛风湿,又能强腰膝的药物是()
《旧约》的文学特色。
某新建项目建设投资为10000万元,其中含可抵扣固定资产进项税850万元,每年营业收入为5000万元(不含税)。原材料及燃料动力费用为2000万元(不含税),增值税税率均为17%,生产负荷除第1年为80%,第2年90%外,其余各年均为100%,则项目投产第
1959年,()发表了《“得过且过”的科学》一文,从政策研究角度对理性—综合方法与渐进方法进行比较,提出其优势所在,促进了渐进规划方法的发展。
()核对属于账证核对的内容。
巴塞尔委员会将银行资产按照流动性高低分为四类:最有流动性的资产、其他可在市场上交易的证券、商业银行可出售的贷款组合和流动性最差的资产。下列不属于流动性最差的资产的是()。
甲股份有限公司(以下简称“甲公司”)的注册会计师在对其2×16年财务报表进行审计时,就以下事项的会计处理与甲公司管理层进行沟通:(1)2×16年1月1日,甲公司将一项管理用固定资产以432.95万元的价格出售给某租赁公司(非关联公司)。2×16年1月
国内安全保卫,是对()的侦查和防范工作。
通感,是指把不同感官的感觉沟通起来,借联想引起感觉转移,“以感觉写感觉”。通感技巧的运用,能突破语言的局限,丰富表情达意的审美情趣,收到增强文采的艺术效果。根据上述定义,下列句子没有运用通感的是:
Mozartwasachildgenius—hewrotemusicalnotesbeforehecouldwritewordsandbegancomposingmusicwhenhewasfouryearsol
最新回复
(
0
)