How deep is the ocean?
The ocean has an average depth of approximately 3.7 kilometres (or 2.3 miles). A calculation from satellite measurements in 2010 put the average depth at 3,682 metres (12,080 feet). However, at the time only about 10% of Earth's seafloor had been mapped to high resolution, so this figure is only an estimate.
Ocean depth is divided into zones: littoral, bathyal, abyssal and hadal. The deepest part of the ocean, the hadal zone, is anywhere deeper than six kilometres.
Challenger Deep, in the Mariana Trench, is the deepest point in the ocean known so far, at approximately 11 kilometres - deeper than Mount Everest is tall. The trench is located in the western Pacific Ocean.
The extreme depth of the Mariana Trench and other oceanic trenches is caused by subduction - where on the boundary of two converging tectonic plates, one descends down into Earth's mantle, creating a deep trough.