How can we be so sure that the Marianas Trench is the deepest place on Earth when much of the ocean hasn’t been explored yet?

Question

How can we be so sure that the Marianas Trench is the deepest place on Earth when much of the ocean hasn’t been explored yet?

In: Geology

Answer 1

The whole thing has been mapped by satellites that can measure ocean depth. Most of the ocean is yet to have somebody physically go there and look around to see what lives there and such, but the topology is not unknown.