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
Directions: In this part, you will have 15 minutes to go over the passage quickly and answer the questions on Answer Sheet 1. Fo
Directions: In this part, you will have 15 minutes to go over the passage quickly and answer the questions on Answer Sheet 1. Fo
admin
2012-12-13
71
问题
Directions: In this part, you will have 15 minutes to go over the passage quickly and answer the questions on Answer Sheet 1.
For questions 1-4, mark
Y (for YES) if the statement agrees with the information given in the passage;
N (for NO) if the statement contradicts the information given in the passage;
NG (for NOT GIVEN) if the information is not given in the passage.
For questions 5-10, complete the sentences with the information given in the passage.
Earth’s Beginnings: The Origins of Life
Earth is the only planet we know of that can support life. This is an amazing fact considering that it is made out of the same matter as other planets in our solar system, was formed at the same time and through the same processes as every other planet, and gets its energy from the sun.
To a universal traveler, Earth may seem to be a harmless little planet in the far reaches of one of billions of spiral galaxies in the universe. It has an average size star of average brightness and is joined by eight other planets—which support no known life forms—in its solar system.
However, Earth is a planet teeming with vitality and is home to billions of plants and animals that share a common evolutionary track. How and why did we get here? What processes had to take place for this to happen? And where do we go from here? The fact is, no one has been able to come close to knowing exactly what led to the origins of life, and we may never know. After 4.5 billion years of Earth’s formation and evolution, the evidence may have been lost. But scientists have made significant progress in understanding what chemical processes that may have led to the origins of life.
There are many theories, but most have the same general perspective of how things came to be the way they are. Following is an account of life’s beginnings based on some of the leading research and theories related to the subject, and of course, fossil records dating back as far as 3.5 billion years ago.
Earth’s Beginnings
Earth began to form over 4.5 billion years ago from the same cloud of gas (mostly hydrogen and helium) and interstellar dust that formed our sun, the rest of the solar system and even our galaxy. In fact, Earth is still forming and cooling from the galactic implosion that created the other stars and planetary systems in our galaxy, a process which began about 16 billion years ago as the Milky Way began to form.
As our solar system began to come together some 6—7 billion years ago, the sun formed within a cloud of dust and gas that continued to shrink upon itself by its own gravitational forces. This caused it to undergo the fusion process and give off light, heat and other radiation. During this process, the remaining clouds of gas and dust that surrounded the sun began to form into smaller lumps called planetesimals, which eventually formed into the planets we know today.
The Earth went through a period of catastrophic and intense formation during its earliest beginnings about 4.5—4.6 billion years ago. By 3.8 to 4.1 billion years ago, Earth had become a planet with an atmosphere (not like our atmosphere today!) and an ocean. This period of time of Earth’s formation is referred to as the pre-Cambrian Period. The pre-Cambrian is divided into three parts: the Hadean, Archean and Proterozoic Periods.
Pre-Cambrian Period
The Earth formed under so much heat and pressure that it formed as a molten planet. For nearly the first billion years of its formation—called the Hadean Period (or "hellish" period)—Earth was bombarded continuously by the remnants of the dust and debris—like asteroids, meteors and comets—until it formed into a solid sphere, fell into an orbit around the sun, and began to cool down.
As Earth began to take solid form, it had no free oxygen in its atmosphere. It was so hot that the water droplets in its atmosphere could not settle to form surface water or ice. Its atmosphere was also so poisonous that nothing would have been able to survive.
Earth’s atmosphere was formed mostly from the outgassing of such volatile compounds as water vapor, carbon monoxide, methane, ammonia, nitrogen, carbon dioxide, hydrochloric acid and sulfur produced by the constant volcanic eruptions that besieged the Earth. It had no flee oxygen.
About 4.1 billion years ago, the Earth’s surface—or crust—began to cool and stabilize, creating the solid surface with its rocky terrain. Clouds formed as the Earth began to cool, producing enormous volumes of rain water that formed the oceans. For the next 1.3 billion years (3.8 to 2.5 billion years ago), called the Archean Period, first life began to appear (at least as far as our fossil records tell us... there may have been life before this!) and the world’s land masses began to form. Earth’s initial life forms were bacteria which could survive in the highly toxic atmosphere that existed during this time. In fact, all life was bacteria during the Archean Period.
Toward the end of the Archean Period and at the beginning of the Proterozoic Period, about 2.5 billion years ago, oxygen-forming photosynthesis began to occur. The first fossils, in fact, were a type of blue-green algae that could photosynthesize.
Some of the most exciting events in Earth’s history and life occurred during this time which spanned about two billion years until about 550 million years ago. The continents began to form and stabilize, creating the supercontinent Rodinia about 1.1 billion years ago. (Rodinia is widely accepted as the first supercontinent, but there were probably others before it.) Although Rodinia is composed of some of the same land fragments as the more popular supercontinent, Pangea, they are two different supercontinents. Pangea formed some 225 million years ago and would evolve into the seven continents we know today.
Free oxygen began to build up around the middle of the Proterozoic Period—around 1.8 billion years ago—and made way for the emergence of life as we know it today. This event, of course, created conditions that would not allow most of the existing life to survive and thus made way for the more oxygen dependent life forms.
By the end of the Proterozoic Period, Earth was well along in its evolutionary processes leading to our current period, the Holocene Period, also known as the Age of Man. Thus, about 550 million years ago, the Cambrian Period began. During this period, life "exploded," developing almost all of the major groups of plants and animals in a relatively short time. It ended with the massive extinction of most of the existing species about 500 million years ago, making room for the future appearance and evolution of new plant and animal species.
And then, about 498 million years later—2.2 million years ago—the first modem human species emerged.
Most theories about the evolution of Earth have the same general point of view.
选项
A、Y
B、N
C、NG
答案
A
解析
转载请注明原文地址:https://kaotiyun.com/show/FzI7777K
0
大学英语六级
相关试题推荐
AnattempttorescuetheAmerican______endedindisasterwhenahelicoptercrashed.
Sleep______canresultinmentaldisorderssuchasmemoryloss,obsession.
Mostpeopletendtothinktheyaresoefficientattheirjobthattheyare________.
Thenativesarenotedfortheir______andkindnesseventostrangers.
Thepublishingcompanyofferstheirstaffopportunitiesfor______indecision-making.
Byastrange______thekingwasassassinatedontheveryspotwherehisgrandfatherhadbeenkilled.
Thereissupposedtobeasafety________whichmakesitimpossiblefortrainstocollide.
Isyourfamilyinterestedinbuyingadog?Adogcanbeahappy【36】toyourfamily,butifyouchoosethewrongkindofdog,the【
A、Itisthesameasself-respect.B、Itistotallydifferentfromself-respect.C、Itistoevaluatepositivelyandholdhighrega
Thereasonsbehindthelackofphysicalactivityinvariousnations______(除了汽车和电视的普及外,还包括都市化).
随机试题
一个10cm×20cm的矩形射野,其等效方野边长为
对于上述合同,下列说法中正确的是()。任何一个单位都有自己的组织结构,每个岗位都有自己的责任和权力,如果超越了,自己的权力范围而为民事行为,这种行为()。
对于游客提出涉及国家法律明令禁止,或有驳于我国传统道德标准的问题时,导游人员要采取什么方式回答()
案例:段老师觉得每次收发学生的作业进行评分,效果欠佳,形式单一.于是对教学评价方式方法进行改进。具体做法是(1)指导学生建立美术学习电子档案袋,将学生作业进行拍照存档。并标注作业时间、题目等信息,同时附上《美术作业评价表》。评价表有四项内容:教师
很长一段时间整个中国互联网界都对Twitter所代表的微博客持______态度,除了担心监控系统的执行效率问题外,更关键在于,大家认为Twitter这种即时群体书写平台除了一定的社会关系网络价值外,短期内并不能带来实际的商业______收益。填入横
当前,随着经济全球化、城市化进程加快和人们生产生活方式的改变,非遗赖以生存的文化________环境正在发生变化,作为传统文化的非遗受到现代文明的________,一些依赖口传心授方式传承的非遗正在消失,一些非遗项目后继乏人,面临人亡艺绝的危险。依次填入画
古代法律中的“公罪”是指()的犯罪。
埃斯库罗斯
王某与李某系单位同事,王某为一般职工,李某为部门经理。某日,王某与李某所在单位被盗,李某个人被盗债券价值1万元。李某向公安机关报案后,又在单位内召集职工说明政策,要求作案者投案自首。王某怀疑是其同学张某所为,因为张某曾到单位来找过王某。王某感到李某对其产生
兴趣
最新回复
(
0
)