What is the deepest portion of the earth?
The deepest point in any ocean is the Mariana Trench (aka Challenger Deep) in the western Pacific Ocean at 11,033 metres deep.
A deep ocean trench is a portion of the Earth's crust in which a tectonic plate is being subducted (pushed down) below another plate. At the border of the 2 plates there is a down turned portion of the uppermost plate along the uppermost edge of the subducting plate. Within this area a trench is formed and as correctly pointed out, this plate interaction does cause the deepest places on Earth.