The average ocean is about 3,682 meters (12,080 feet) deep, as of November 2026. Part of it is the twilight zone, from about 200 to 1,000 meters (656 to 3,280 feet) down, where only a little light reaches. Far down in the deep ocean it is dark, because sunlight does not reach there.

Below 1,000 meters is the midnight zone, which reaches down to about 4,000 meters. It has no sunlight at all and stays near 4 degrees Celsius. Below it is the abyss. It is cold and dark with crushing pressure, yet animals and microbes live there. The hadal zone is the deepest part of the ocean. It is found in deep trenches, below about 6,000 meters (19,700 feet).

The deepest place in the ocean is called Challenger Deep. It is in the Pacific Ocean. It lies in the Mariana Trench, a long, deep trench in the floor of the western Pacific Ocean, near Guam. NOAA gives its depth as about 10,935 meters (35,876 feet) in November 2026. In 1960, Jacques Piccard and Don Walsh were the first people to go to the bottom of it, in a deep-diving craft called Trieste.

Alvin is a research submarine that carries up to three people to the deep sea floor. It was commissioned in 1964. Scientists also use robot submarines called ROVs, steered from a ship, to explore the deep ocean.

You may have heard that we already have a map of the whole ocean floor. In fact, as of April 2026, only about 28.7 percent of the ocean floor had been mapped in detail. Scientists think most kinds of ocean life have not yet been discovered or named.

You may have heard that nothing makes light down there. In fact, many animals in the deep sea make their own light. Making light like this is called bioluminescence. Deep-sea animals use their light to find food, to find mates and to protect themselves. A deep-sea anglerfish has a glowing lure that dangles in front of its mouth, and the glowing tip holds bacteria that make light.

A giant squid has eyes as big as dinner plates. Giant squid can be up to about 13 meters (43 feet) long. In 2012, scientists from Japan filmed a giant squid alive in its deep-sea home for the first time.

A hydrothermal vent is a place on the sea floor where very hot water comes out of the ground. At vents and some other places on the deep sea floor, tiny microbes make food from chemicals instead of from sunlight. This is called chemosynthesis. Giant tube worms live at deep-sea vents and can grow almost five feet long. They have no mouth or stomach. Bacteria living inside them make food from vent chemicals for the worm.

Marine snow is a shower of bits of food that slowly falls from the upper ocean to the deep. Many deep-sea animals eat it. A vampire squid has two long, sticky threads. It catches bits of falling marine snow with them. Then it pulls the bits through its arms to eat. When a whale sinks to the sea floor at the end of its life, it becomes a whale fall: food and a home for many deep-sea animals.

You may have heard that nothing could live in the deepest part of the ocean. In fact, snailfish live deeper than any other fish scientists have found, in the deepest trenches. The deepest fish ever seen alive was a small snailfish filmed at 8,336 meters (27,349 feet) in a trench near Japan in August 2022.

Words to know

• chemosynthesis: food from chemicals
• bacteria: tiny living things
• abyss: deep dark zone
• bioluminescence: living light
• hydrothermal: hot-water