1. Mariana Trench, Pacific Ocean The Pacific is the largest ocean in the world, at more than 60 million square miles, so it is perhaps not surprising that the greatest depth on the planet is in the Pacific Ocean, in the Mariana Trench, which extends 35,827 feet below sea level. At the very bottom of the trench, the pressure is more than 1000 times that of standard atmospheric pressure at sea level. The trench are named for the nearby Mariana Islands, which, in turn, were named for Queen Mariana of Austria, the wife of Spain’s King Philip IV, who reigned in the 17th Century.