While thousands of climbers have successfully scaled Mount Everest, the highest point on Earth, only two people have descended to the planet’s deepest point, the Challenger Deep in the Pacific Ocean’s Mariana Trench. Located in the western Pacific east of the Philippines and an average of approximately 200 kilometers east of the Mariana Islands, the Mariana Trench is a crescent-shaped scar in the Earth’s crust that measures more than 2,550 kilometers long and 69 kilometers wide on average. The distance between the surface of the ocean and the trench’s deepest point—the Challenger Deep, which lies about 322 kilometers southwest of the U.S. territory of Guam. If Mount Everest were dropped into the Mariana Trench, its peak would still be more than 1.6 kilometers underwater. The Mariana Trench is part of a global network of deep troughs that cut across the ocean floor. They form when two tectonic plates collide. At the collision point, one of the plates dives beneath the...