from BBC Learning English.

I'm Sam. And I'm Neil. The 20th of

July 1969 was a big day in

history. Do you know why, Sam? Wasn't that when Neil Armstrong

first set foot on the Moon? Right. But it's often forgotten

that some of the most dramatic

photographs taken on the

Apollo space mission weren't

of the Moon at all - they

were of Earth. It wasn't

until we went to the Moon

that we really saw the

size of Earth's oceans

and named ourselves,

the Blue Planet. Despite most of our planet

being covered by water,

the ocean remains of place

of unexplored mystery, of

sea monsters like

Moby Dick, and the Kraken.

In this programme, we'll

be diving into the

deep seas, seeing some

of its strange sights,

and as usual, learning

some related vocabulary too. But before that I have a

question for you, Sam.

You were right when you

said that most of the

Earth is covered

by water. But do you

know exactly how much

of the Earth's surface

is ocean? Is it: a) 50 percent?  

b) 60 percent? or, c) 70 percent?  

Well, it is called

the Blue Planet, so

I ll say c) 70 percent. OK. I'll reveal the answer

later in the programme.

The first thing to say

about the deep ocean is

that the rules of life

down there are very

different from the rules

on land. Sunlight

cannot reach the very

bottom of the ocean,

a place between two and

three kilometres down

known as the 'deep abyss',

so it totally dark and

extremely cold. And the

weight of water creates

massive amounts of pressure. This extreme environment is

stranger than fiction, and

home to things which seem

to be from another planet;

things like hydrothermal

vents - volcanic hot springs

which break through the

ocean floor. Oceanographer,

Alex Rogers, joined an

expedition which discovered

a hydrothermal vent in

the ocean near Antarctica.

He told his story to BBC

World Service programme,

Discovery: Well, the first problem is

actually finding them

because they cover a very

small area so it's

literally like trying to

find a needle in a haystack,

but when you do come across

them, I mean, the deep ocean

is food limited, so life

is quite thin on the ground,

and then suddenly your

camera just stumbles into

this area where there is

just abundant life all

over the sea floor and

around these vents. Alex says that finding

these small thermal vents

at the bottom of the ocean

is like finding a needle

in a haystack, an idiom

meaning almost impossible

to find because the area

you have to search

is so large. Because there's no sunlight

on the ocean floor, it's

hard for plants and

creatures to survive, so

forms of life are thin

on the ground - there are

only a few of them. Alex

cannot find anything to film

with his camera, until

suddenly he nears the vent

and sees plants and animals

everywhere. Here, there is

more than enough, or

abundant life. To picture a hydrothermal

vent, imagine an underwater

volcano. Billowing clouds of

what looks like smoke

heat the seawater to a

temperature of 386 degrees C.

This creates a warm

environment of all kinds

of weird and wonderful

creatures, including vent

mussels, tube worms and

blind 'yeti crabs', so

called because of their

hairy claws, some of

which get cooked because

the water is so hot. What's amazing is that

while these vents may be

as old as Earth itself,

they were only discovered

in the 1970s. So, are

there more mysteries hiding

in the deep ocean? That's

the question BBC World

Service's, Discovery, asked

marine biologist, Kerry Howell.

Here's what she said. I have absolutely no doubt

that there is plenty more to

discover down there. It's really

vast, I mean it's quite hard to

get your head around how vast

the deep sea is, and it is

most of our planet. So... and

we've barely scratched the

surface of exploration of this

unique environment, and if

you think that vents were

only discovered in the 70s,

you know, there's great

potential for a lot else

to come, I think. We've only

been exploring this

environment for the last

150 years, I mean. Before

that we didn't think

there was any life down

there at all. So, it's

a very young science is

Deep Sea biology. And so,

there's... yeah, there's

a lot more to discover.

I have no doubt. In terms of ocean

exploration Kerry thinks

we've only scratched the

surface - found out a

little bit about something,

but not enough to

fully understand it. That's because the ocean

is vast - extremely big.

So vast, in fact, that it's

hard to get your head

around it, or difficult

to really understand. But how vast, exactly,

Sam? In my question I asked

how much of the Earth's

surface is covered by water.  

And I said it was c) 70 percent. Which was the correct answer!

Well, 71 percent to be precise,

but either way it's hard to

get your head around or

difficult to fully understand. OK, we'd better recap the

other vocabulary too,

starting with the idiom,

finding a needle in a haystack

meaning that something is

almost impossible to find

because you have to

search so widely for it. If something is thin on the

ground, there's very little

of it, but if it's abundant,

there's plenty or

more than enough. When you only scratch the

surface, you find out a

little about something,

but not enough to

fully understand it. And finally, vast is

another way of saying

extremely large,

huge or enormous. Unlike the vast oceans,

our time is limited to

just six minutes and

it's up. So, join us

again soon for more

amazing adventures and,

of course, useful

vocabulary, here at 6 Minute

English. Goodbye for now! Goodbye!