The ocean is deep, but how deep? Scientist know that the deepest part of the ocean is a place called the Mariana Trench. In 2010 the trench was measured at 36,070 feet deep. As a comparison the highest point on earth is 29,020 feet tall. It's called Mount Everest in the country of Nepal. That makes the Mariana Trench over a mile deeper than Everest is tall. The reason the ocean is so deep at this spot is that two pieces of the ocean floor are colliding. One piece is actually sliding underneath the other. The trench is deepest where the two pieces meet.