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Hello, this is 6 Minute English
from BBC Learning English. I'm Beth.
And I'm Phil.
Phil, do you believe
there's life on other planets?
Well, there's a lot of other planets,
so yeah, I think there must be.
Yeah, I agree.
Well, it's a question that interests
American astrophysicist Adam Frank,
who discussed it
with his colleague Gavin Schmidt,
director of NASA's Institute
for Space Studies.
Here, Adam recalls their conversation
for BBC World Service programme
CrowdScience:
We know that there's been
no other civilisation on Earth,
and he stopped me and said,
How do you know that?
And my jaw just dropped down
to the floor.
Adam's jaw dropped – an idiom for when
someone looks shocked and surprised.
Could there have been a technologically
advanced civilisation before us,
here on Earth?
It may sound weird
but this idea has a scientific name.
Here is Caroline Steel, presenter
of BBC's CrowdScience, to explain:
The Silurian hypothesis proposes
that if there was
a technologically advanced civilisation
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, we'll be discussing
the Silurian hypothesis:
the idea that a technologically
advanced civilisation
existed before us on Earth
but vanished without leaving a trace.
As usual, we'll be learning
some useful new words and idioms,
and remember –
you'll find all the vocabulary
on our website,
bbclearningenglish.com.
But first,
I have a question for you, Phil.
Human civilisation is thousands
of years old
but the planet itself is much older.
So, how old does do scientists think
the Earth is?
Is it: a) 3.5 billion years,
b) 4.5 billion years,
or c) 5.5 billion years.
I'm going to guess
c) 5.5 billion years.
OK. Well, we will find the answer out
later in the programme.
To believe a technologically
advanced civilisation 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 Silurian hypothesis,
as he explains here to BBC
World Service programme CrowdScience.
Most things are not fossilised.
It's only a tiny fraction of Earth's
life that has ever become fossilised.
So, imagine that you have
a 10,000-year-long civilisation,
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 10,000-year-old civilisation is
the blink of an eye –
an idiom meaning
a very short period of time.
In other words, older civilisations
might have existed on Earth
but not for long enough
to leave fossilised evidence.
However, not everyone is convinced by
Adam's ideas.
Evidence of our own civilisation,
including plastics
and man-made materials like concrete,
is already being layered
into the Earth's crust,
and these are going to last
a very long time.
So, surely a technologically
advanced civilisation from prehistory
would have left similar marks.
Well, here's Adam Frank again,
answering these objections on BBC
World Service programme CrowdScience.
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,
30 or 40 papers,
then you have a consensus.
You're like, OK.
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 civilisations on Earth
is so mysterious,
it's OK 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, 5.5 billion years,
and I'm afraid you were wrong, Phil.
It's 4.5 billion years.
OK. Let's recap the vocabulary we've
learnt, 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 or 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 idiom the blink of an eye
means a very short period of time.
And finally,
a consensus is a general agreement.
Once again, our six minutes are up
but if you're keen for more,
then head over to our website,
bbclearningenglish.com,
where you'll find a worksheet
and a quiz for this episode.
See you again soon.
But for now, it's goodbye!
Goodbye.
Vocabulary
Word 1 of 12prehistoric civilisations
phrase
1:44
"civilisations that may have existed long before recorded human history."
More Listening Practice
About this lesson
Explore the scientific hypothesis of whether a non-human civilisation could have existed on Earth millions of years ago.