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
98
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 following statements about the water on Venus is true?
选项
A、The water evaporated because of the high temperatures.
B、The water became frozen in the polar regions.
C、Only a little water is left in small lakes on the surface.
D、Rain does not fall because there is no atmosphere.
答案
A
解析
"Venus has some traces of water vapor in its atmosphere, but it is much too hot for liquid water to survive." Choice B is not correct because the water transformed to vapor, not ice. Ice refers to our moon, not to Venus. Choice C is not correct because the lakes or oceans evaporated quickly. Choice D is not correct because the airless atmosphere refers to Mercury, not to Venus.
转载请注明原文地址:https://www.kaotiyun.com/show/4yyO777K
0
托福(TOEFL)
相关试题推荐
TheStudyofChimpanzeeCultureA.Afterstudyingthesimilaritiesbetweenchimpanzeesandhumansforyears,researchershav
SECTION1Questions1-10Questions1-3Listentothetelephoneconversationbetweenastudentandtheownerofaparaglidings
【1】Thecarusesa______lockingsystem.
Betweenwhattimesistheroadtrafficlightest?airconditioning
Betweenwhattimesistheroadtrafficlightest?Whatwillbetheextracostofmodifyinghouses?
Betweenwhattimesistheroadtrafficlightest?Whichdayoftheweekhastheleasttraffic?
TheprofessoralreadyknowssomethingaboutClarefromher______.
TheprofessoralreadyknowssomethingaboutClarefromher______.
Thereneedstobeabalancebetweentheneedsof______livingindevelopedenvironmentsandthepreservationofnaturalhabitat
随机试题
吉兰-巴雷综合征危及患者生命的最主要的临床表现是
某有限责任公司股东会决定解散该公司,其后股东会、清算组下列行为中不违反我国法律规定的行为的是()。
甲市为乙省政府所在地的市。关于甲市政府行政机构设置和编制管理,下列说法正确的是:(2011—卷二—98,任)
0.04090的有效位数为()。
工程项目的设计工作一般分为初步设计和施工图设计两个阶段,重大项目和技术复杂项目,可根据需要增加( )阶段。
需申请到货地检验检疫机构鉴定的残损商品,应在索赔期满( )前申请鉴定。
国内某机电生产型企业,为增值税一般纳税人。2015年该企业发生的业务如下:(1)取得产品销售收入2700万元,其他业务收入200万元,销售成本1000万元,其他业务成本50万元。(2)“管理费用”账户列支100万元,其中:业务招待费30万元、新产品技术
主刑的特点是既不以独立适用,也不以附加适用。()
在考生文件夹下,打开文档WORD.DOCx,按照要求完成下列操作并以该文件名(WORD.DOCX)保存文档。将标题段文字(“盐的世界”)设置为三号黑体、居中、字符间距加宽4磅、加绿色(标准色)底纹。
Mr.andMrs.Davishadfourchildren.OneSaturdayMrs.Davissaidtoherhusband,"Thechildrenhaven’tgotanylessontoday,a
最新回复
(
0
)