Part I
Professor: OK. I want to go over the different types of meteorites and what we've learned about them from the formation of earth and the 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 originating on earth, just in different proportions.
But that makes it easier to identify something as a meteorite as opposed to just a terrestrial rock. So to talk about where meteorites come from, we need to talk about comets and asteroids, which basically, they are 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 comets and asteroids now, but we will come back later and do that.
问题是，陨石特别有趣的是它们虽然来自行星际空间，但它们却由与地球上的物质相同的化学元素组成，只是比例不同而已。
1. meteoroid 流星体; meteor 流星;meteorite 陨石; comet 彗星; asteroid 小行星; planet 行星; star 恒星; satellite 卫星; black hole 黑洞; worm hole 虫洞
2. the thing is
used to introduce an important fact, reason or explanation 事实是；主要原因是
E.g.: I'm sorry my assignment isn't finished. The thing is, I've had a lot of other work this week.
对不起，我的任务没完成。主要原因是我这星期有许多其他工作要做。
3. interplanetary|ˌɪntərˈplænəteri|
adj. between planets 行星间的
E.g.: By definition , interplanetary travel is travel between bodies in a given star system.
星系旅行是指在给定的行星系统内在不同星体间的旅行。
4. originate|əˈrɪdʒɪneɪt|
verb. to happen or appear for the first time in a particular place or situation 起源；发源；发端于
E.g.:The disease is thought to have originated in the tropics.
这种疾病据说起源于热带地区。
5. terrestrial|təˈrestriəl|
adj. connected with the planet Earth 地球的；地球上的
E.g.: Newton proposed that heavenly and terrestrial motion could be unified with the idea of gravity.
牛顿提出天体和地球的运动可以用万有引力来统一解释。
6. debris |dəˈbri:|
noun. pieces of wood, metal, brick, etc. that are left after sth has been destroyed 残骸；碎片；破片
E.g.: Emergency teams are still clearing the debris from the plane crash.
各抢救小组仍在清理失事飞机的残骸。
7. out of order
not allowed by the rules of a formal meeting or debate 违反规程的；不合乎（会议或辩论）规则的
E.g.: His objection was ruled out of order.
他的反对被裁定为违反会议规则。
8. in depth
in a detailed and thorough way 全面；深入；详细
E.g.: I haven't looked at the report in depth yet.
我还没有细看这份报告。
Part II
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? 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, in the inner solar system between Jupiter and Mars to be precise, we've got the asteroid belt, which contains about 90 percent 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 like, uh, 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.
还记得我们讨论过太阳系中的两类行星吗？它们在成分上是如何不同的？像火星和地球这样主要由岩石和金属组成的类地行星，还有像木星这样的大型气态巨行星。
1. Mercury 水星, Venus 金星, Earth 地球, Mars 火星, Jupiter 木星, Saturn 土星, Uranus 天王星, Neptune 海王星
2. analogous |əˈnæləgəs|
adj. similar in some way to another thing or situation and therefore able to be compared with it 相似的；类似的
E.g.: Sleep has often been thought of as being in some way analogous to death.
人们常常认为睡眠在某种意义上来说类似死亡。
3. namely |ˈneɪmli|
adv. used to introduce more exact and detailed information about sth that you have just mentioned 即；也就是
E.g.: We need to concentrate on our target audience, namely women aged between 20 and 30.
我们须针对我们的目标听众，即年龄在20到30岁之间的妇女。
4. orbit|ˈɔ:rbɪt|
verb. to move in an orbit (= a curved path) around a much larger object, especially a planet, star, etc. 沿轨道运行；围绕…运动
E.g.: The earth takes a year to orbit the sun.
地球绕太阳一周要一年的时间。
5. methane 甲烷; carbon dioxide 二氧化碳; carbon monoxide 一氧化碳; oxygen 氧气; hydrogen 氢气; nitrogen 氮气; hydrogen sulfide 硫化氢
6. collection |kəˈlekʃn|
noun. a collection of things is a group of things 一堆，一群(东西)
E.g.: Wye Lea is a collection of farm buildings that have been converted into an attractive complex.
“怀河草地”是一处由农舍改造而成的赏心悦目的建筑群。
Part III
Both comets and asteroids are, typically are smaller than planets. An even smaller type of interplanetary debris is the meteoroid. And it's from the meteoroids that we get meteors and meteorites. Roids are, for the most part anyway, they're 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're called meteors. Most of them are very small and they burn up soon after entering 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.
当这些碎片进入地球大气层时，它们就变得如此特别以至于得到了一个特殊的名字：它们被称为流星。
1. for the most part
mostly; usually 多半；通常
E.g.: The contributors are, for the most part, professional scientists.
投稿者大多是专业科学家。
Part IV
Now, we've 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 are rocks. And like rocks, they are 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. Any one guess why? Look at their names. What do you think iron meteorites consist of?
Student: Mostly iron?
Professor: Yeah! Iron and some nickel, both of which are metals. And if you're trying to find metal?
我们已经对它们进行了足够多的分析，以了解它们的成分，其中大部分来自小行星，尽管少数可能来自彗星。
1. mineral|ˈmɪnərəl|
noun. a substance that is naturally present in the earth and is not formed from animal or vegetable matter, for example gold and salt. Some minerals are also present in food and drink and in the human body and are essential for good health. 矿物；矿物质
E.g.: the recommended intake of vitamins and minerals
维生素和矿物质的建议摄入量
2. account for
to be a particular amount or part of sth （数量上、比例上）占
E.g.: The Japanese market accounts for 35% of the company's revenue..
日本市场占该公司收入的35%。
3. nickel 镍; gold 金; silver 银; copper 铜; lead 铅; aluminum 铝; mercury 汞; potassium 钾; sodium 钠; calcium 钙
Part V
Student: Oh, metal detectors!
Professor: Right! Thank you! At least that's part of it. Stone meteorites, if they lie around exposed to the weather for a few years, well, they're 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 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'll be, they are iron meteorites, or the stony iron kind, even though they only make up about 5 percent of the meteorite material on the ground.
石质陨石，如果被暴露在天气中风雨暴晒几年，因为它们是由岩石制成的，所以它们最终看起来将与普通的陆地岩石几乎没有区别，即那些本就源自地球的岩石。
1. detector|dɪˈtektə(r)|
noun. a piece of equipment for discovering the presence of sth, such as metal, smoke, explosives or changes in pressure or temperature 探测器；侦察器；检测器
E.g.: The detector must be operationally simple, reliable and robust.
探测器必须操作方便, 可靠而牢固。
2. indistinguishable |ˌɪndɪˈstɪŋgwɪʃəbl|
adj. if two things are indistinguishable , or one is indistinguishable from the other, it is impossible to see any differences between them 无法分辨的；无法区分的
E.g.: This enzyme would make the filtration of beer easier.
这种酶会使啤酒更容易过滤。
3. spot |spɑ:t|
verb. to see or notice a person or thing, especially suddenly or when it is not easy to do so 看见；看出；注意到；发现
E.g.: No one spotted that the gun was a fake.
没有人留意到那是一支假枪。
4. make up
to form sth 形成；构成
E.g.: Women make up 56% of the student numbers.
女生占学生人数的56%。
