\" \" The Mariana Trench is loaded with weird and wonderful sea life. It's the Mariana Trench, an underwater gash in Earth's crust that's five times longer than the Grand Canyon and much, much deeper. In fact, the Mariana Trench is the deepest part anywhere in the Earth's oceans. AdvertisementThe trench forms where two tectonic plates (jigsaw-puzzle-shaped pieces of Earth's crust) crunch into each other. The water pressure in the trench is nearly 1,000 times greater than at sea level.