BBC 英语学习 在人类出现之前，地球上是否存在文明

Hello. This is 6 min English from BBC, learning English.

I'm Beth, and I'm Phil. Phil.

Do you

believe there is life on other planets?

Well, there's a lot of other planets, so

I think it must be. Yeah, I agree.

Well, it's a question that interests American astrophysicist Adam Frank, who discussed it with a colleague, gavin Schmidt, director of nasa's Institutes for Space Studies.

Here, adam recalls their conversation for BBC World Services and PROGRAMM crowd science.

We know that there's been no other civilization on Earth.

And he stopped at me and said, how do you know that?

And the judge just dropped down to the floor.

Adams jaw dropped an idiom for when someone looked shocked and surprised, could there have been a technologically advanced civilization before us here on Earth?

It may sound weird, but this idea has a scientific name.

Here is Caroline Steel, presenter of bbc's Crowd Science, to explain The Siluian hypothesis proposes that if there was a technologically advanced civilization hundreds of millions of years ago, we wouldn't be able to find traces of it.

A hypothesis is an idea which explains how something happens and can be tested to find out if it's correct.

In this episode, will be discussing the Siluian hypothesis, the idea that a technologically advanced civilization existed before us on Earth but vanished without leaving a trace.

As usual, will be learning some useful new words and idioms.

And remember, you'll find all the vocabulary on our website, bbc learning english dot com.

But 1st, I have a question for you phil Human civilization is thousands of years old, but the planet itself is much older.

So how old do scientists think the Earth is?

Is it A three and a half billion years?

B Four and a half billion years, or see, five and a half billion years?

I'm gonna go see five and a half billion years.

Okay, well, we will find the answer out later in the program.

To believe a technologically advanced civilization existed on Earth hundreds of millions of years ago, most people would probably want evidence.

We have evidence about other species from the past, such as the dinosaurs, from fossils, the remains of prehistoric plants or animals that have been preserved in rock for a very long time.

But according to Adam Frank, fossils won't help prove the Siluian hypothesis, as he explains here to BBC World Service program Crowd Science, most things are not fossilized.

It's only a tiny fraction of earth's life that has ever become fossilized.

So imagine that you have a 10000 year long civilization, which is a blink of the eye for geology.

That's too short to really create a lot of fossils.

Adam argues that only a tiny fraction, meaning a very small amount, of life on Earth, has turned into fossil in geological time.

Even a 10000 year old civilization is the blink of an eye an India, meaning a very short period of time.

In other words, older civilizations might have existed on Earth, but not for long enough to leave fossilized evidence.

However, not everyone is convinced by adam's ideas.

Evidence of our own civilization, including plastics and man made materials like concrete, is already being layered into the earth's crest, and these are going to last a very long time.

So surely a technologically advanced civilization from prehistory would have left similar marks.

Well, here's Adam Frank again answering these objections on BBC World Service program crowd signs.

What happens is somebody else will pick up on their work, either affirming it and showing new evidence for it, or pushing back on it.

And once you get to, like, 20, 3040 papers, then you have a consensus.

You're like, okay, we've really, really looked at this, and now we know Adam welcomes new evidence, even evidence which contradicts his ideas, as part of the scientific method needed to prove a hypothesis, right or wrong.

It's how scientists form a consensus, meaning a general agreement about the issue.

Personally, I think the idea of prehistoric civilizations on Earth is so mysterious, it's okay to keep an open mind.

Now. Isn't it time you revealed the answer to your question?

Beth? I think it is. I asked you, how old do scientists think the Earth is?

You said five and a half billion years.

And I'm afraid you were wrong, phil it's four and a half billion years.

OK, let's recap the

vocabulary we've learned, starting with the

idiom My jaw dropped, which is

used to say, someone looks very shocked and surprised.

A hypothesis is a suggestion that's proposed to explain something, which can then be tested to see if it's true.

Fossils are the remains of prehistoric plants and animals that have been preserved in rock for a very long time.

A tiny fraction of something is a very small amount of it, the idium, the blink of an eye means a very short period of time.

And finally, a consensus is a general agreement.

Once again, our 6 min are up, but if you came for more, then head over to our website, bbc learning english dot com, where you'll find a worksheet and a quiz for this episode.

See again soon, but for now, it's goodbye.

Goodbye. 6 min English from BBC, learning english dot com.

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