Most of the ocean is deeper than sunlight can reach. Switch on the lights and come down.
Bioluminescence is light made by a living thing, using a chemical reaction inside its own body. It is cold light, so it never burns, and far down in the sea it is often the only light there is.
In some places on the sea floor, seawater sinks into cracks near undersea volcanoes, gets heated deep inside the Earth, and shoots straight back out. Scientists have measured that water at about 750 degrees Fahrenheit, more than three times hotter than boiling water.
A sperm whale looks for its food by diving. It goes down to around 2,000 feet again and again, and one dive can last about 45 minutes, all on the single breath it took at the surface.
Below about 660 feet the ocean turns cold and heavy. Down deep the average temperature is around 39 degrees Fahrenheit, close to the inside of a fridge, and the water presses down hundreds of times harder than the air does at the beach.
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