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
"Four Stages of Planetary Development" Planetary Development The planet Earth has passed through four-stages of planetary
"Four Stages of Planetary Development" Planetary Development The planet Earth has passed through four-stages of planetary
admin
2018-07-24
65
问题
"Four Stages of Planetary Development"
Planetary Development
The planet Earth has passed through four-stages of planetary development. All terrestrial planets pass through these same stages to some degree, but some planets evolved further or were affected in different ways.
The Four Stages
The first stage of planetary evolution is differentiation, the separation of material according to density. Earth now has a dense core and a lower-density crust, and that structure must have originated very early in its history. Differentiation would have occurred easily if Earth were molten when it was young. Two sources of energy could have heated Earth. First, heat of formation was released by in-falling material. A
meteorite
hitting Earth at high velocity converts most of its energy of motion into heat, and the impacts of a large number of meteorites would have released tremendous heat. If Earth formed rapidly, this heat would have accumulated much more rapidly than it could leak away, and Earth was probably molten when it formed. A second source of heat requires more time to develop. The decay of radioactive elements trapped in the Earth releases heat gradually; but, as soon as Earth formed, that heat began to accumulate and helped melt Earth. That would have helped the planet differentiate.
While Earth was still in a molten state, meteorites could leave no trace, but in the second stage in planetary evolution, cratering, the young Earth was battered by meteorites that pulverized the newly forming crust. The largest meteorites blasted out crater basins hundreds of kilometers in diameter. As the solar nebula cleared, the amount of debris decreased, and after the late heavy bombardment, the level of cratering fell to its present low level. Although meteorites still occasionally strike Earth and dig craters, cratering is no longer the dominant influence on Earth’s geology. As you compare other worlds with Earth, you will discover traces of this intense period of cratering, on every old surface in the solar system.
The third stage, flooding, no doubt began while cratering was still intense. The fracturing of the crust and the heating produced by radioactive decay allowed molten rock just below the crust to well up through fissures and flood the deeper basins. You will find such flooded basins with solidified lava flows on other worlds, such as the moon, but all traces of this early lava flooding have been destroyed by later geological activity in Earth’s crust. On Earth, flooding continued as the atmosphere cooled and water fell as rain, filling the deepest basins to produce the first oceans. A Notice that on Earth flooding involves both lava and water, a circumstance that we will not find on most worlds. B
The fourth stage, slow surface evolution, has continued for the last 3.5 billion years or more. C Earth’s surface is constantly changing as sections of crust slide over each other, push up mountains, and shift continents. D Almost all traces of the first billion years of Earth’s geology have been destroyed by the active crust and erosion.
Earth as a Planet
All terrestrial planets pass through these four stages, but some have emphasized one stage over another, and some planets have failed to progress fully through the four stages. Earth is a good standard for comparative
planetology
because every major process on any rocky world in our solar system is represented in some form on Earth.
Nevertheless, Earth is peculiar in two ways. First, it has large amounts of liquid water on its surface. Fully 75 percent of its surface is covered by this liquid; no other planet in our solar system is known to have such extensive liquid water on its surface. Water not only fills the oceans but also evaporates into the atmosphere, forms clouds, and then falls as rain. Water falling on the continents flows downhill to form rivers that flow back to the sea, and in so doing, the water produces intense erosion. You will not see such intense erosion on most worlds. Liquid water is, in fact, a rare material on most planets. Your home planet is special in a second way. Some of the matter on the surface of this world is alive, and a small part of that living matter is aware. No one is sure how the presence of living matter has affected the evolution of Earth, but this process seems to be totally missing from other worlds in our solar system. Furthermore, the thinking part of life on Earth, humankind, is actively altering our planet.
Glossary
meteorite: a mass that falls to the surface of a planet from space planetology: the study of planets
What can be inferred about radioactive matter?
选项
A、It is revealed by later activity.
B、It generates intense heat.
C、It is an important stage.
D、it floods the planet’s crust.
答案
B
解析
Because radioactive decay "releases heat" and "helped melt Earth," it must be concluded that radioactive matter generates intense heat. Choice A is not correct because all traces of early lava flooding caused by radioactive heating have been destroyed. Choice C is probably true, but the relative importance of the stages is not mentioned in the passage. Choice D is not correct because the heating, not the flooding, is caused by radioactive decay.
转载请注明原文地址:https://kaotiyun.com/show/btfO777K
0
托福(TOEFL)
相关试题推荐
Whichattitudeisassociatedwiththefollowingpeopleduringtheconversation?ChooseSIXanswersfromtheboxandwritetheco
Whichattitudeisassociatedwiththefollowingpeopleduringtheconversation?ChooseSIXanswersfromtheboxandwritetheco
Completethenotesbelow.WriteNOMORETHANTWOWORDSforeachanswer.CLIMATEANDARCHITECTURECasesandexamplesarefrompra
Completethenotesbelow.WriteNOMORETHANTWOWORDSforeachanswer.CLIMATEANDARCHITECTURECasesandexamplesarefrompra
Completethenotesbelow.WriteNOMORETHANTWOWORDSforeachanswer.CLIMATEANDARCHITECTURECasesandexamplesarefrompra
Completethesentencesbelow.WriteNOMORETHANTHREEWORDSforeachanswer.Thelandfordevelopmenthasnotbeenusedforov
Completethenotesbelow.WriteONEWORDONLYforeachanswer.DevelopmentStudiesDevelopmentStudiesattemptstounderstand-
Anactivistforwomen’s(rights),LeonoraO’Reillypromotedwomen’svocationaltraining(besides)foughtfor(increased)(wages)
"ConquestbyPatents"→Patentsareaformofintellectualpropertyrightsoftentoutedasameanstogive’incentiveandrew
随机试题
下列选项中,不属于组织文化发展趋势的是()
关于民事法律关系,下列说法正确的是()
利巴韦林的化学名为乙胺丁醇的化学名为
患者,女,48岁,体检发现子宫黏膜下肌瘤询问护士该病最常见的临床表现,护士告知
下列修测种类中,不属于基本图修测方案的是()。
某公司(甲方)综合楼工程,地下室1层,地上9层,总建筑面积33000m2,箱形基础,框架剪力墙结构。基坑采用土钉墙支护,于5月份完成了土方作业,并制定了雨期施工方案。计划雨期主要施工部位:基础SBS改性沥青卷材防水工程、基础底板钢筋混凝土工程、地下室1层至
()对企业应当纳税的税种、税目、税率以及纳税时限和处罚等作出了规定。
从前,有两个饥饿的人得到一位长者的恩赐:一个人要了一篓鱼,另一个要了鱼竿,他们就分路了。得到鱼的人原地就用篝火煮了鱼,吃了个精光,不久便饿死了。另一个人则提着鱼竿忍饥挨饿向海边走去,可当他看到大海时,最后一点力气也使完了,他眼巴巴地带着无尽的遗憾撒手人间。
某市A区因经济开发需要,决定征用该区某村的集体土地300亩。因土地补偿问题协商不成,该村有80户村民不服,打算申请行政复议。下列哪一说法是正确的?()
对于逻辑表达式((bl&b2)||in),需要_______个测试用例才能完成条件组合覆盖。
最新回复
(
0
)