Mount Everest is the highest point on Earth, rising to 29,035 feet (8,850 meters). But what’s the deepest point? For that, we have to go below sea level, to the western Pacific Ocean and the Mariana Trench, which is 36,201 feet (11,034 meters) deep.

Curiosity contributor Susan Sherwood plumbed the history of expeditions to the depths of the Mariana Trench.

The "Challenger Deep" section of the Mariana Trench was first visited in a 1960 U.S. naval expedition. Navy Lt. Donald Walsh and Swiss scientist Jacques Piccard (son of the boat’s designer) traveled there in a bathyscaphe, a submersible designed to withstand the tremendous pressure (almost 17,000 pounds per square inch) it would encounter. Blimp-like, the Trieste was 50 feet long and 12 feet in diameter (15 meters long, 3.7 meters in diameter). Its lower compartment, less than 7 feet (2 meters) across, contained the divers and equipment.

The vessel was highly buoyant, so it carried 9 tons (8 metric tons) of iron shot; this allowed it to sink at a rate between 1 1/2 and 3 feet (0.45 and 0.9 meters) per second. After nearly five hours, the descent was complete. The divers remained on the bottom for 20 very chilly minutes. The temperature inside the bathyscaphe was 45 degrees Fahrenheit (7.2 degrees Celsius). Releasing weight, the Trieste returned to the surface slowly, taking three hours and 17 minutes to do so.

On March 25, 2012, a second vessel reached the bottom of the trench, this time a solo journey. James Cameron, of Titanic (1997) fame, co-designed a small submersible to take him to the Mariana Trench. As part of a cooperative project with National Geographic, Cameron descended alone in the Deepsea Challenger, crammed into a tiny section of the 24-foot-long (7 meter) glass foam watercraft. Unlike the earlier explorers, Cameron took cameras (traditional and 3-D).

The Deepsea Challenger experienced somewhat different pressure trials than its long-ago predecessor. The submersible descended and ascended faster and stayed at the bottom longer (about three hours). By releasing steel weights, the craft rose to the surface in just 70 minutes.

Other mogul-adventurers will likely follow. What began more than half a century ago as a naval operation has seemingly evolved into a journey for private enterprise.