The deepest part of the ocean is the Mariana Trench, an oceanic trench located in the Pacific Ocean near the island nation of Guam. At its deepest point, known as the Challenger Deep, the Mariana Trench is almost seven miles (11 kilometers) below sea level. Just to put that in a frame of reference, if we were to shave Mount Everest off the surface of the Earth and drop it into the Mariana Trench, it would disappear, buried in over a mile of water.

As you might imagine, the pressure in the Mariana Trench is extreme: about 1,000 times the atmospheric pressure at sea level. Organisms like humans which are accustomed to life at sea level would implode within fractions of a second if exposed to that depth, and the creatures which live in the Mariana Trench demonstrate a number of unusual adaptations which help them cope with the pressure. Algae, bacteria, marine worms, and an assortment of other unusual creatures live in the total darkness and extreme cold of the Mariana Trench, interrupted only occasionally by survey submarines sent to explore the deepest part of the ocean for science.

This incredibly deep ocean trench has formed at what is known as a convergent plate boundary. The deepest part of the ocean is formed by the subduction of the Pacific Plate under the Philippine Plate. To get an illustration of what the trench looks like, you can slide one of your hands under the other. Right along the boundary where your hands meet, you will notice that a notably deep trough is formed; if you magnify that significantly, you get an idea of what the deepest part of the ocean looks like.

The first survey of the Mariana Trench was undertaken in 1951 by a British team on board the Challenger II. Since the team discovered the deepest point of the trench, the Challenger Deep was named after them. A United States Navy bathysphere visited the bottom of the trench in 1960 with two men on board. Oceanographers liken this expedition to the first moon landing, because of the immense amount of preparation and danger involved, and some like to point out that more is known about the surface of the moon than the deepest part of the ocean.

The Mariana Trench isn't the only deep ocean trench, although it is certainly the deepest, extending to twice the average depth of the world's oceans. Given the extreme conditions at the Mariana Trench, it's unlikely that you will be spending any time there, but if you do, you will be able to see a fascinating array of marine organisms which have only been seen by a handful of human beings.