首页
登录
职称英语
"Four Stages of Planetary Development" Planetary Development
"Four Stages of Planetary Development" Planetary Development
游客
2024-01-04
28
管理
问题
"Four Stages of Planetary Development"
Planetary Development
→ In our study of the planet Earth, we will find a four-stage history of planetary development. The moon and all the terrestrial planets have passed through these stages, although differences in the way the planets were altered by these stages have produced dramatically different worlds. The moon, for example, is much like Earth, but its evolution has been dramatically altered by its smaller size. As we explore the solar system, we will discover not entirely new processes but rather familiar effects working in slightly 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.
Differentiation would have occurred easily if Earth were molten when it was young. Two sources of heat could have heated Earth. First, heat of formation would be created by in-falling material. A
meteorite
hitting Earth at high velocity converts most of its energy of motion into heat, and the in-falling of a large number of meteorites could release tremendous heat.
If Earth formed rapidly, this heat would have accumulated much more rapidly than it could leak away, and Earth may have been 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 would have begun to accumulate and could have helped melt Earth to facilitate differentiation. Most of Earth’s radioactive elements are now concentrated in the crust, where they continue to warm and soften the rock layers.
Earth formed by material falling together, but meteorites could have left no trace until a crust solidified. Once Earth had a hard surface, the meteorites could form craters. This second stage in planetary evolution, cratering, was violent. The heavy bombardment was intense because the solar nebula was filled with rocky and icy debris, and 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 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 we compare other worlds with Earth, we will discover traces of this intense period of cratering, the heavy bombardment, 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 caused by radioactive decay allowed molten rock just below the crust to well up through fissures and flood the deeper basins. We will discuss such flooded basins 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 activecrust and erosion.
Earth as a Planet
All terrestrial planets pass through these four stages, so in that respect, Earth is a good basic reference planet for comparative planetology. Some planets have emphasized one stage over another, and some planets have failed to progress fully through the four stages. Nevertheless, Earth is a good standard of comparison. Every major process on any rocky world in our solar system is represented in some form on Earth.
On the other hand, 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 and no other planet in our solar system is known to have such extensive liquid water on its surface. Furthermore, some of the matter on the surface of this world is alive, and a small part of that living matter is aware. We do not know 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.
Glossary
meteorite: a mass that falls to the surface of a planet from space
planetology: the study of planets [br] An introduction for a short summary of the passage appears below. Complete the summary by selecting the THREE answer choices that mention the most important points in the. passage. Some sentences do not belong in the summary because they express ideas that are not included in the passage or are minor points from the passage. This question is worth 2 points. There are four stages of development for the terrestrial planets. ______ ______ ______
Answer Choices
A. All rocky planets go through different stages in their evolution because of variations in composition.
B. In spite of several unique features, the Earth is a good example of how a planet proceeds through the stages.
C. Fewer meteorites fall to Earth now than in the earlier stages of the planet’s evolutionary history.
D. About three quarters of the surface of the Earth is submerged by the water in its oceans.
E. Differentiation and cratering are early stages that are influenced by in-falling meteorites.
F. Flooding includes both lava and water, while slow surface evolution causes shifting in the crust.
选项
答案
EFB
解析
summarizes the passage. Choice A is not correct because the stages are the same. Choice C is true, but it is a minor point that refers to major point E. Choice D is true, but it is a minor point that refers to major point F.
转载请注明原文地址:https://tihaiku.com/zcyy/3333017.html
相关试题推荐
EngineeringforsustainabledevelopmentTheGreenhouseProject(Himalayanmounta
EngineeringforsustainabledevelopmentTheGreenhouseProject(Himalayanmounta
EngineeringforsustainabledevelopmentTheGreenhouseProject(Himalayanmounta
EngineeringforsustainabledevelopmentTheGreenhouseProject(Himalayanmounta
EngineeringforsustainabledevelopmentTheGreenhouseProject(Himalayanmounta
EngineeringforsustainabledevelopmentTheGreenhouseProject(Himalayanmounta
Bothsocialfactorsandthedevelopmentof【L31】________havebeenimpo
Bothsocialfactorsandthedevelopmentof【L31】________havebeenimpo
Bothsocialfactorsandthedevelopmentof【L31】________havebeenimpo
Bothsocialfactorsandthedevelopmentof【L31】________havebeenimpo
随机试题
TheotherdayIwaslisteningtoaChristianradioprogramonthewaytothe
A.只受剪力 B.只受弯矩 C.同时受弯矩、剪力 D.同时受弯矩、剪力和轴
国际上,将BIM模型的深度分为几级?()A.3 B.4 C.5 D.6
常见人体水解酶对其天然底物K值A.与其他合成底物的K值相同 B.<10mol/
引起牙齿病理性移位的主要因素是()A.急性牙周膜炎 B.女性激素水
曹操《短歌行》原文 对酒当歌,人生几何!譬如朝露,去日苦多。 慨当以
以下有关处方调配要点的叙述中,最关键的事项是A:认真审核处方 B:准确调配药品
例行巡视中,对于引流线应检查()。(A)伸缩节无变形、散股及支撑螺杆脱出现象。
各种运输方式内外部的各个方面的构成和联系,就是( )。 A.运输系统
某县人口50万,约80%居民以河水为饮用水,该县设有一传染病科的综合医院,其污水
最新回复
(
0
)