What is the ocean layer found deeper than about 6,000 metres called?

The hadal zone is the ocean layer found deeper than about 6,000 metres.

Named after Hades, the ancient Greek underworld, the hadal zone occupies the deepest parts of the ocean, chiefly within trenches and other narrow depressions. It extends from roughly 6,000 metres to the seafloor at the greatest depths, including the Challenger Deep in the Mariana Trench.

Conditions are extreme: pressure rises by about one atmosphere for every 10 metres of seawater, temperatures are generally low, and sunlight is absent. Nevertheless, specialized organisms live there, including amphipods, sea cucumbers, microbes, and hadal snailfish in some trenches. Organic matter sinking from upper waters provides an important food supply.

The hadal zone is often confused with the abyssal zone. The abyssal region generally covers deep ocean floors from about 4,000 to 6,000 metres, whereas hadal environments are deeper and usually associated with trenches. Only a small fraction has been directly explored.