OLogy

1. Scientists divide oceans into horizontal zones, like a layer cake. 2. Billions move up from the deep ocean to feed every night.

In the ocean you see a much greater variety of creatures if you move up or down than by moving from side to side.

The sunlit zone, near the top, is rich in life. Algae bloom here, providing huge quantities of food for the animals that live here, and for the billions of deep-sea animals that rise to feed here every night, and then return to the deep at dawn. This vertical migration is the largest mass movement of life on Earth. And it happens every night!

As you dive deeper, to the colder, darker twilight zone, there's less life. Zooplankton and sea snow provide most of the food for the animals that live here.

Way down deep is the icy-cold dark zone, where signs of life are rare. The pressure of the water would crush a human. It's pitch-black here because no sunlight penetrates. The only light is provided by bioluminescence — glowing lights on animals' bodies.