Part 4 - They that go down to the sea

This week, we get a little deep. Around 40% of the world's population lives within 100km of the sea. Humankind's history is profoundly connected to the world's oceans. We fished, traveled, sailed and explored them, pretty much as soon as we could. And we've never really stopped. Our planet's oceans are perhaps the greatest potential natural resource we have, and yet we literally know more about the far side of the moon or the surface of Mars than we do our own ocean floor. In this episode we're going to go down, deep, deep down, all the way through the most alien place on Earth, full of strange creatures, extreme conditions and remarkable facts - the ocean!.