The deep sea is broadly defined as the ocean depth where light begins to
fade, at an approximate depth of 200 metres (656 feet) or the point of
transition from continental shelves to continental slopes. Conditions
within the deep sea are a combination of low temperatures, darkness and
high pressure. The deep sea is considered the least explored Earth biome
as the extreme conditions make the environment difficult to access and
explore.
In 1960, the bathyscaphe Trieste descended to the bottom of the Mariana Trench near Guam,
at 10,911 m (35,797 ft; 6.780 mi), the deepest known spot in any ocean.