The Mariana Trench or Marianas Trench is located in the western Pacific Ocean about 200 kilometres (124 mi) east of the Mariana Islands and it is the deepest oceanic trench on Earth.

It is crescent-shaped and measures about 2,550 km (1,580 mi) in length and 69 km (43 mi) in width. The maximum known depth is 10,984 metres (36,037 ft) (± 25 metres [82 ft]) (6.825 miles) at the southern end of a small slot-shaped valley in its floor known as the Challenger Deep. However, some unrepeated measurements place the deepest portion at 11,034 metres (36,201 ft).If Mount Everest were hypothetically placed into the trench at this point, its peak would still be underwater by more than two kilometres (1.2 mi).

At the bottom of the trench, the water column above exerts a pressure of 1,086 bars (15,750 psi), more than 1,071 times the standard atmospheric pressure at sea level. At this pressure, the density of water is increased by 4.96%. The temperature at the bottom is 1 to 4 °C (34 to 39 °F).

In 2009, the Marianas Trench was established as a US National Monument. Monothalamea have been found in the trench by Scripps Institution of Oceanography researchers at a record depth of 10.6 kilometres (6.6 mi) below the sea surface. Data has also suggested that microbial life forms thrive within the trench.