Official 13 Set 6

纠错
  • Q1
  • Q2
  • Q3
  • Q4
  • Q5
  • Q6
置顶

Meteorites

纠错
  • Q1
  • Q2
  • Q3
  • Q4
  • Q5
  • Q6
What is the main topic of the lecture?
  • A. The major differences between meteors and meteorites

  • B. The origins of comets and asteroids

  • C. The nature and origin of meteorites

  • D. The similarities between objects in the inner solar system

显示答案 正确答案: C

我的笔记 编辑笔记

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    NARRATOR:Listen to part of a lecture in an astronomy class.

    MALE PROFESSOR:Ok, I wanna go over the different types of meteorites, and what we have learned from them about the formation of Earth and solar system.Uh... the thing is, what's especially interesting about meteorites is that they come from interplanetary space, but they consist of the same chemical elements that are in matter originated on Earth, just in different proportions.But that makes it easier to identify something as a meteorite, as it opposed to... to just a terrestrial rock.So to talk about where meteorites come from, we need to talk about comets and asteroids, which basically, they’re basically made up of debris left over from the origin of the solar system 4.6 billion years ago.

    Now I’m going a bit out of order here, um, I’m not going to go into any depth on uh comets and asteroids now, but we’ll come back later and do that.For now, I'll just cover some basic info about them.

    Ok, comets and asteroids… it might help if you think of…Remember we talked about the two classes of planets in our solar system, and how they differ in composition? …[reviewing] the terrestrial planets like Mars and Earth…composed largely of rocks and metals, and the large gas giants like Jupiter.Well, the solar system also has two analogous classes of objects, smaller than planets…namely, asteroids and comets.Relatively near the Sun and the inner solar system, between Jupiter and Mars to be precise, we've got the asteroid belt, which contains about 90% of all asteroids orbiting the Sun.These asteroids are... uh... like the terrestrial planets, in that they are composed mostly of rocky material and metals.

    Far from the Sun, in the outer solar system, beyond Jupiter's orbit, temperatures are low enough to permit ices to form out of water and... and out of gases are like methane and carbon dioxide.Loose collections of these ices and small rocky particles form into comets.So comets are similar in composition to the gas giants.Both comets and asteroids are... typically are smaller than planets.

    An even smaller type of the interplanetary debris is the meteoroid.And it’s from meteoroids, we get meteors and meteorites.Meteoroids are…for the most part anyway…they are just smaller bits of asteroids and comets.When these bits enter Earth’s atmosphere, well, that makes them so special that they get a special name. They are called “meteors.”Most of them are very small, and they burn up soon after entering the Earth's atmosphere.The larger ones that make it through the atmosphere, and hit the ground are called meteorites.So meteorites are the ones that actually make it through.

    Now we have been finding meteorites on Earth for thousands of years, and we've analyzed enough of them to learn a lot about their composition.Most come from asteroids…though a few may have come from comets…so essentially they’re rocks, and like rocks they’re mixtures of minerals.They are generally classified into three broad categories: stones, stony irons and irons.

    Stone meteorites, which we refer to simply as, uh, stones, are almost entirely rock material.They actually account for almost all of the meteorite material that falls to Earth.But even so, it's rare to ever find one, I mean, it's easier to find an iron meteorite or stony iron.Anyone guess why?Look at their names. What do you think iron meteorites consist of?

    FEMALE STUDENT:Mostly iron?

    MALE PROFESSOR:Yeah, iron and some nickle, both of which are metals. [slowly, with rising intonation consistent with giving a hint] And if you’re trying to find metal?

    FEMALE STUDENT:Oh, metal detectors!

    MALE PROFESSOR:Right, thank you. At least that's a part of it.Stone meteorites, if they lie around, exposed to the weather for a few years, well, they are made of rock, so they end up looking almost indistinguishable from common terrestrial rocks...ones that originated on Earth.So it's hard to spot them by eye.But we can use the metal detectors to help us find the others, and they are easier to spot by eye.So most of the meteorites in collections, uh, in museums, they will be... they are iron meteorites, or the stony iron kind, even though they only make up about 5% of the meteorite material on the ground.

  • 旁白:请听一段天文学课上的演讲。

    教授:好的,我要讲一下各种不同的陨星,以及我们从这些陨星上获取的关于地球构造和太阳系的信息。额,陨星特别有趣的一点是,这些陨星来自行星际空间,但是他们包含着同样的起源于地球的化学元素,只是成分所占比例不同而已。但这使得我们可以更容易辨认出陨星,而不会将其当做一种地球上的岩石。说到陨星的来源,我们就需要讨论下彗星和小行星,基本上,它们是由46 亿年前太阳系诞生以来留下的碎片组成的。

    我有点次序颠倒了,恩,我不会详细深入讲彗星或小行星,我们以后再讲。从现在开始,我会只讲一些基本信息。

    好的,彗星和小行星,它可能帮助你想到......记得我们说过太阳系中的两类行星吗?还有他们在成分上有什么不同的?类地行星,像火星或地球,大部分是由岩石和金属构成的,还有像木星这样的大型气态巨行星。嗯,太阳系中还有两种相类似的星体分类,比行星要小,那就是小行星和彗星。相对而言,这些星体更接近太阳和太阳系内部,确切地说,处于木星和火星之间。我们知道小行星带的存在,这里面有90%的小行星是绕着太阳运行的。这些小行星,额,就像是类地行星,他们主要是由岩石和金属构成的。

    在远离太阳的地方,在太阳系外延,木星轨道之外,那里的气温很低,足以使某些水分凝结成冰,而且,释放出像甲烷和二氧化碳这样的气体。这些冰块和小型的岩石微粒会集合起来,形成彗星。所以彗星的成分和气体巨星的成分是相类似的。彗星和小行星都要比行星小很多。

    一种更小的星际碎片是流星体。而从这些行星体中会有流星和陨石。流星体在大多数情况下,它们是小行星和彗星的一小部分。当这些碎片进入地球大气层之后,这就使它们变的特别,以至于会有一个特别的名字,称为流星。大部分流星都体积很小,在进入大气层之后会很快燃烧起来。那些体积较大,进入大气层之后直击地面的流星便叫做陨石。因此陨石其实就是那些穿透大气层到达地球表面的行星体。

    如今我们发现陨石的历史已经有几千年了,我们已经对其进行了足够的分析,了解了很多关于陨石的成分。知道大部分是来自小行星,尽管有些陨石是来自彗星。所以,本质上讲,这些陨石就是岩石。他们是各种矿物的混合物。基本上被分为三大类:石头,陨铁石和铁块。

    石陨石,我们简单称为,额,石头,几乎完全是岩石材料。事实上它们几乎占到所有落到地球表面陨石物质的全部。但即便如此,也很少能找到石陨石。我是说,找到一块铁陨星或陨铁石会更容易点。有人知道为什么吗?看看这些陨石的名字,你们觉得陨铁石包括什么呢?

    学生:大部分是铁吧?

    教授:是的,铁和镍,两者都是金属成分。而如果你正试图找某些金属材料的话?

    学生:哦!金属探测器!

    教授:好的,谢谢。至少这是其中的一部分。石陨石,如果暴露在天气中好几年,嗯,由于他们都是由石头构成的,所以基本上这些石陨石跟那些普通的地球上的石头并无两样。而要靠肉眼来察觉这些星体是比较难的。但是我们能用金属测探器帮助我们找到其他流星体,这些能更容易通过肉眼看到。因此大部分在博物馆里收集的陨石,它们都是铁陨星,或是陨铁石,即便它们只占到地面上的陨星材料的5%。

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  • 本题对应音频:
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    音频1
    解析

    题型分类:主旨题
    原文定位:

    OK, I want to go over the different types of meteorites, and what we've learned from them about the formation of earth and the solar system. Uh, the thing is, what's especially interesting about meteorites is, that they come from inter-planetary space, but they consist of the same chemical elements that are in matter originating on earth, just in different proportions. But that makes it easier to identify something as a meteorite as opposed to...to just a terrestrial rock.
    选项分析:
    这篇文章的主旨需要听完全文进行概括总结,最开始教授说要讲不同种 类的 meteoroids,但是后来用了大篇幅去解释它的起源,然后又给了meteoroid 的分类,最后才讲到了 meteorite,并对其进行分类阐述,所以其实讲座的main topic 是meteorite。其他的选项都太细节了,因此,选项C正确。


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