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 exampl
"Life in Our Solar System" Although we can imagine life based on something other than carbon chemistry, we know of no exampl
admin
2012-01-14
63
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 possi- bilities 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℃ (-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 0n 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.
Which of the sentences below best expresses the information in the highlighted statement in the passage? The other choices change the meaning or leave out important information.
选项
A、Life on Mars was found as a result of research in many cases.
B、The evidence did not demonstrate that there was life on Mars in the past.
C、Many cases of life were concluded in the history of Mars.
D、The conclusion was that only one instance of life on Mars was verified.
答案
B
解析
... the evidence did not demonstrate paraphrases "the results did not confirm."
转载请注明原文地址:https://kaotiyun.com/show/eyyO777K
0
托福(TOEFL)
相关试题推荐
EducationPhilosophyA.Althoughwelackaccuratestatisticsaboutchildmortalityinthepre-industrialperiod,wedohave
TheStudyofChimpanzeeCultureA.Afterstudyingthesimilaritiesbetweenchimpanzeesandhumansforyears,researchershav
SECTION1Questions1-10Questions1-3Listentothetelephoneconversationbetweenastudentandtheownerofaparaglidings
Betweenwhattimesistheroadtrafficlightest?Whichisthecorrectconstructionforacousticdoubleglazing?
Betweenwhattimesistheroadtrafficlightest?airconditioning
Betweenwhattimesistheroadtrafficlightest?Whichdayoftheweekhastheleasttraffic?
TheprofessoralreadyknowssomethingaboutClarefromher______.
Thereneedstobeabalancebetweentheneedsof______livingindevelopedenvironmentsandthepreservationofnaturalhabitat
Johnwasfirstinterestedinthesubjectbecauseofsomething______
Johnwasfirstinterestedinthesubjectbecauseofsomething______
随机试题
管理会计和财务会计的主要区别有()
所有权是物权的一种,属于()
湿热下注,扰动精室而致遗精的首选方为( )湿热下注,宗筋弛纵而致阳痿的首选方为( )
A、有效性B、均一性C、专一性D、稳定性E、安全性能有目的地调节人的生理机能体现药品的
实行限额设计,应根据()对各设计专业的投资进行分配,并按分配的投资限额控制设计。
综合检验设备制造和设备安装质量的重要环节是()。
选择单据号为0002(单据类型为应收借项)的应收单,生成凭证。
如何评价北美独立战争?
事业单位的专用基金主要包括修购基金、职工福利基金、医疗基金、住房公积金以及投资基金等。()
若有定义语句:char,*s1="OK",*s2="ok";以下选项中,能够输出"OK"的语句是
最新回复
(
0
)