Ocean: Secrets of the Deep

From a certain point in outer space, above the Pacific Ocean, the Earth appears entirely blue.

It is the presence of liquid water in such vast quantities that marks the planet out from its neighbours in the solar system. The oceans spawned the earliest life forms, and they continue to sustain all terrestrial creatures - mankind included.

And not simply through the water cycle; the oceans also play a vital role in regulating the Earth's temperature; without them, the planet would be inhospitably hot by day and cold by night.