But the explorer said he was surprised there were so little visible signs of life in the Mariana Trench.

BBC: Science & Environment

While places like the Mariana Trench were once thought to be of little interest, there has been a recent resurgence of scientific interest in the deep.

BBC: James Cameron back on surface after deepest ocean dive

It's up for grabs, who will be first to descend to the bottom of the legendary Mariana Trench and back, in roughly the time it takes to drive from San Francisco to Los Angeles.

WSJ: A New Wave of Ocean Explorers | Marvels

The billionaires are bankrolling expeditions to reach the deepest place in the ocean, a spot called the Challenger Deep that lies at the bottom of the Mariana Trench, seven miles below the surface of the South Pacific.

FORBES: Branson And Schmidt Race To The Bottom Of The Ocean

In 1960 Don Walsh, along with Jacques Piccard, undertook an eight-and-a-half hour decent in the bathyscaphe Trieste to the deepest part of the ocean, the 10, 911 metre (36, 000ft) Challenger's Deep in the Mariana Trench off the coast of the Phillipines.

BBC: Voyage to the 'real' North Pole

Barely a month after filmmaker James Cameron piloted a newfangled submersible to the bottom of the Mariana Trench, audiences can get an inside look at the historic expedition that for the first time sent a lone human to the deepest place on Earth.

MSN: Cameron's Historic Deep-Sea Dive Debuts on National TV

While manned exploration had until now seen a 52-year hiatus, scientists have used two robotic unmanned vehicles to explore the Mariana Trench: Japan's Kaiko made a dive there in 1995 and the US-based Woods Hole Oceanographic Institution's vessel Nereus explored the deep in 2008.

BBC: James Cameron back on surface after deepest ocean dive