This is an excerpt from the BTN story DEEP SEA EXPLORATION
http://www.abc.net.au/btn/story/s4530...

The Ocean is actually split up into 3 zones. The first is the Sunlight Zone. That's where a lot of the most wellknown fish live and is about as far down as most humans can go. At 200 metres, you reach the Twilight Zone, where light starts to disappear. At more than 1000 metres down, sunlight disappears completely. This is the Midnight Zone. It's a cold, dark place that we still don't know much about. It's also where huge, freaky sea life starts appearing, like the giant squid. But it's still not even close to the bottom in most places on earth. The lowest point is a whopping 11,000 metres down. That's about the same depth as stacking 36 Eiffel towers on top of each other. That place is called Challenger Deep in the Mariana Trench.