首页
登录
职称英语
What is the main purpose of the lecture? [originaltext] Listen to part of a l
What is the main purpose of the lecture? [originaltext] Listen to part of a l
游客
2025-02-03
34
管理
问题
What is the main purpose of the lecture?
Listen to part of a lecture in an astronomy class.
Professor:
Today we’re gonna talk about something planetary scientists have yet provided a satisfactory explanation for. How was the moon formed? From the samples the Apollo astronauts brought back we know that the moon is about four and a half billion years old and formed about at the same time as the rest of our solar system.
Now there are some theories about how the moon was formed. The first, dating back to the 19th century. It’s called fission theory. Fission means splitting into parts. The theory proposes that Earth spun so rapidly in its early years that a chunk of it broke off and got thrown into space into Earth’s orbit, and that chunk from Earth became the moon. The fission theory was accepted well into the 20th century, but we now know that Earth was spinning at a rate that was much too slow for this kind of fission to occur.
Another theory is the capture theory which goes like this. The moon formed somewhere in the solar system and was captured by Earth’s gravitational field as it was passing by. And it stayed in Earth’s orbit ever since. Now the moon’s chemical composition is different from Earth, so if the moon formed somewhere else this would actually explain why they’re different in composition, right? However, astronomers have a problem with the capture theory because for the moon to be captured into its present orbit, a complex set of circumstances is required, so it’s very unlikely that it happened.
The most widely supported theory today is the giant impact theory. It suggests that the moon formed as a result of an impact onto the young Earth four and a half billion years ago when the young Earth collided with another planetary object. According to this theory the moon formed from debris caused by a giant impact which had gone into orbit around the Earth. The scientific community didn’t jump on this theory right away. You can’t test it since it’s impossible to find traces of an impact with the Earth that far back. And remember the Earth and moon have different compositions and densities. The moon’s density is much lower than that of the Earth or any other terrestrial planets. This indicates that the moon lacks high density iron and doesn’t have a big iron core like Earth, which was confirmed by measurements taken during the Apollo moon landing.
But wouldn’t the moon and the Earth be similar in composition and density if the moon formed from rock fragments that were ejected from Earth? So astronomers came up with ideas to explain some of the inconsistencies the theory presents. For instance, the idea that by the time the giant impact happened Earth’s iron had already migrated toward its center, its core, and so the debris that was blown from Earth came from an outer layer which was depleted of iron. Okay, that would explain why Earth has a large iron core and the moon doesn’t.
But we don’t know for sure whether Earth’s core had already formed when the collision occurred. The next step was to use advanced computer technology to simulate the giant impact, an impact that would produce a moon that lacks iron. The researchers who performed the simulations developed different models from a variety of scenarios and came up with some interesting results. According to one model, a collision with an object, 10% of Earth’s mass, about the size of the planet Mars, could in fact account for an iron-poor moon. The model also suggests that the moon formed towards the end of Earth’s formation. This is important because if the moon formed early in Earth’s history, it would have accumulated more iron-rich material.
As convincing as it may sound, the giant impact theory isn’t proven to everyone’s satisfaction since several questions remain unanswered. On the other hand, it is very attractive because it’s consistent with our idea of how planets were assembled. We think collisions played a big role when the planets in our inner solar system formed. We think that during the final stages of the formation of rocky planets, planetary embryos smashed into each other, creating larger planets.
选项
A、To compare the composition of the moon with the composition of Earth
B、To explain the significance of moon samples obtained by Apollo astronauts
C、To discuss theories about the early development of the solar system
D、To discuss problems with explanations for the origin of the moon
答案
D
解析
题目问讲座的主要目的。讲座一开始,教授就提到了这次讲座主要谈论的话题:How was the moon formed?“月球是如何形成的?”随后,他提到了三个解释月球起源的理论,并讲述了每个理论的问题。因此,D项“讨论关于月球起源的几个解释有什么问题”正确。虽然讲座有解释月球和地球的成分的不同之处,但这只是讲座的一小部分内容,不足以概括主题,故排除A项。同样,虽然讲座提到了阿波罗号宇航员从月球带回了样本,但这只是细节信息,同样不足以概括主题,也排除B项。C项“讨论关于太阳系早期发展的理论”没有依据。
转载请注明原文地址:https://tihaiku.com/zcyy/3941742.html
相关试题推荐
Whatisthemainpurposeofthelecture?[br]Accordingtotheprofessor,whatd
Whatisthemainpurposeofthelecture?[br]Accordingtotheprofessor,howdo
Whatisthemainpurposeofthelecture?[br]Whatisonepointtheprofessorma
Whatisthislecturemainlyabout?[br]Priortotheuseofhistologicalanalysi
Whatisthislecturemainlyabout?[br]Whatwouldresearchershaveconcludedif
Whatarethetwospeakersmainlydiscussing?[br]Listenagaintopartoftheco
Whatarethetwospeakersmainlydiscussing?[originaltext]Listeningtopartof
Whydoesthestudentgotoseetheprofessor?[originaltext]Listentoaconversa
Youwillreadashortpassage,listentoatalk,andansweraquestionabout
Youwillreadashortpassage,listentoatalk,andansweraquestionabout
随机试题
ThemanwhoinventedCoca-ColawasnotanativeAtlantan,butonthedayofh
Whenmenandwomengettogether,thereare,ineffect,twoworlds--hisandh
男性,14岁,左上腹被汽车撞后3小时,腹痛、呕吐2次,为胃内容物,自觉头晕乏力、
患儿,男,5岁。猩红热病后20天,出现眼睑水肿,尿呈茶色,血压130/100mm
证券市场融资活动的特点主要有( )。 ①证券市场是一种直接融资 ②证券市场
母线电流差动保护采用电压闭锁元件主要是为了防止区外发生故障时母线电流差动保护误动
l,4,8,12,15,20,22,()A.28 B.25 C.30
假定某高层钢筋混凝土框架结构,共6层,平面规则,在二楼楼面转换,底层框架柱共16
关于标底的说法,错误的是()。A.招标人可以自行决定是否编制标底 B.一
为了便于结算,一个单位可以同时在几家金融机构开立银行基本存款账户。()
最新回复
(
0
)