BBC 6 minute English-The Earth’s core

Transcript of the podcast

NB: This is not a word-for-word transcript

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, Professor of Mineral Physics at the University of Cambridge

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, seismologist at Utrecht University

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 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