Placeholder Image

字幕表 動画を再生する

  • Rob: Hello and welcome to 6 Minute English. I'm Rob.

  • Alice: and I'm Alice. Hello.

  • Rob: Hi there, Alice! Now, have you read any books by Jules Verne?

  • Alice: Yes, I have. Journey to the Centre of the Earth was my favourite book as a child!

  • A German Professor and his two companions climb down a volcano in search of the Earth's centre or core.

  • They visit strange lands inhabited by dinosaurs and giant prehistoric humans,

  • and sail across an underground ocean.

  • Rob: Hmm. Very exciting but it doesn't sound very realistic.

  • How do they get out again?

  • Alice: Well, they shoot to the surface from the mouth of Mount Etna during a volcanic eruption.

  • Rob: Wow! That sounds very uncomfortable!

  • Well, on today's show we're going to discuss

  • what scientists really know about the Earth's core.

  • Alice: Yes. The Earth has a dense inner core surrounded by a fluid outer core.

  • Dense, by the way, means heavy in relation to its size.

  • But, Rob, I've got a question for you as usual:

  • how big do you think the inner core is? Is it the size of ...

  • a) the Moon? b) Jupiter? or c) Mars?

  • Rob: Right! Well, I haven't a clue to be honest so I'm going to take a guess and say c) Mars.

  • Alice: Well, we'll find out later on in the show if you're right.

  • But before we get there, let's find out a bit more about what the Earth is made of.

  • Rob: Well, the Earth has layers, a bit like an onion.

  • Alice: I like your technical language, Rob!

  • Rob: But I'm trying to keep things simple for you, Alice!

  • Alice: Thanks.

  • Rob: It has a thin outer layer or crust where we live.

  • And this includes our continents and the ocean floors.

  • Then beneath that there's another layer called the mantle.

  • And beneath that, is the Earth's core, over 6000km below the surface.

  • Alice: Right. But what's the Earth made of, Rob?

  • Rob: It's a good question. And it depends on which layer you're talking about!

  • The crust and mantle are rock and contain a lot of silicate which is the same stuff that glass is made of.

  • But the outer and inner parts of the core mainly consist of iron.

  • Alice: And the core is very hot. Am I right?

  • Rob: You are indeed. The professor and his companions wouldn't have survived very long down there!

  • The outer core is a swirling mass of molten or liquid metal

  • and it's as hot as the surface of the Sun!

  • Alice: Wow! That must be so hot! Right.

  • Let's listen now to Simon Redfern talking about the inner core and what's happening in there.

  • Simon Redfern: And so over time, the planet has started to cool.

  • And as it cools, eventually at the centre of the Earth,

  • the highest pressure point, we pass over the crystallization temperature

  • the freezing temperature of iron

  • and iron starts to freeze at the centre of the Earth.

  • And you get a crystal of iron right in the middle that starts to grow.

  • Alice: I'm a bit worried that the Earth is freezing in the middle!

  • Rob: Don't worry, Alice!

  • In this case, because of the incredibly high pressure in the core,

  • the freezing point of iron is actually about 6000 degrees!

  • And the iron has been cooling down and crystallizing for a billion years,

  • and at a rate of just half a millimetre every year.

  • Alice: Ah well, yes, that sounds like slow progress.

  • Rob: Certainly. Now moving on,

  • we should also talk about the fact that it's the liquid iron outer core that generates magnetic fields,

  • and it's thanks to these magnetic fields that life on Earth is possible.

  • Let's hear more about this.

  • [Melvyn Bragg talks to Arwen Deuss]

  • Deuss: Well, the magnetic field is very important

  • because it protects us against cosmic radiation. So that's one really...

  • Bragg: How does it do that?

  • Deuss: It just creates a shield, which will just deflect the cosmic rays from the Sun

  • to actually reach us at the surface. So it protects us.

  • Bragg: So it goes up there Deuss: Yeah, so you would see that the radiation

  • kind of goes right into the Earth and not actually reach us.

  • Alice: So there's a magnetic field round the Earth that protects us from the Sun's cosmic rays.

  • I'd like a magnetic field round me.

  • It could be my superpower like in X Men!

  • Rob: Calm down, Magneto.

  • Now the magnetosphere is the area around the Earth in which the Earth's magnetic field is felt.

  • It protects us from the Sun's radiation and the flow of particles,

  • which would otherwise strip away or remove the Earth's atmosphere.

  • Alice: Right, I see. And what does "radiation" mean?

  • Rob: Well, radiation means heat or energy or particles in the form of rays ...

  • in this case, the Sun's rays.

  • Alice: OK. And "deflect"?

  • Rob: To deflect means to make something change direction.

  • Alice: Right, I see. Thank you. Now, Rob, I asked you, do you remember, at the beginning

  • of the show, how big is the Earth's inner core? Is it the size of ... a) the Moon?

  • b) Jupiter? or c) Mars?

  • Rob: Yes, and I had a wild guess and I said c) Mars.

  • Alice: Yes. And I'm afraid that's wrong, Rob. The answer is a) the Moon.

  • Would you like to shape up and tell us which words we learned on the show today?

  • Rob: Of course. Good idea. We heard:

  • core

  • dense

  • crust

  • mantle

  • silicate

  • molten

  • magnetosphere

  • strip away

  • radiation

  • deflect

  • Alice: Yes. Thank you, Rob. Well, that's the end of today's 6 Minute English.

  • We hope you enjoyed our core vocabulary! Please join us again soon.

  • Both: Bye.

Rob: Hello and welcome to 6 Minute English. I'm Rob.

字幕と単語

B1 中級

BBC 6 Minute English September 24, 2015 - The Earth's Core

  • 3657 79
    Adam Huang   に公開
動画の中の単語

前のバージョンに戻す