In what he called a "heckuva ride," James Cameron came "screaming back up" from Earth's deepest point in about 70 minutes Monday, breaking the Pacific Ocean surface on Monday at noon, local time (10 p.m. ET Sunday).

The filmmaker and National Geographic explorer's solo sub dive—the deepest ever—had taken him nearly 7 miles (11 kilometers) underwater to the Mariana Trench's Challenger Deep, southwest of Guam. (See pictures of Cameron's sub.)

Emerging from his cramped "pilot sphere" after surfacing, Cameron flashed two thumbs up, then described what he'd seen.

"It was bleak," he said. "It looked like the moon."

As for life-forms, he said, "I didn't see a fish. ... I didn't find anything that looked alive to me, other than a few [shrimplike] amphipods in the water," he said from aboard the research vessel Mermaid Sapphire. (See pictures of giant amphipods.)

"I didn't feel like I got to a place where I could take interesting geology samples or found anything interesting biologically."

This may be, in part, because a hydraulic fluid leak convinced Cameron to end the mission after about three hours. Previous projections had him surveying and sampling Challenger Deep and its life-forms for as long as six hours.

"I saw a lot of hydraulic oil come up in front of the port. The port got coated with it," he explained.

Cameron had planned to collect rock and animal samples with the sub's mechanical arm, but with the leak, "I couldn't pick anything up, so I began to feel like it was a moment of diminishing returns to go on."

Finally, he said, "I lost a lot of thrusters. I lost the whole starboard side. That's when I decided to come up. I couldn't go any further—I was just spinning in a circle."

Earlier, an issue with the sub's sonar system had scuttled the launch of a baited, unmanned "lander."

The lander was supposed to touch down at Challenger Deep hours before Cameron's arrival and attract deep-ocean predators and scavengers.

But without the sonar system working properly, finding the lander would have been difficult, explained Doug Bartlett, chief scientist for the DEEPSEA CHALLENGE project, a partnership with the National Geographic Society and Rolex. (The Society owns National Geographic News.)

Before the launch, "we decided he's not going to just happen upon" the lander without using sonar, said Bartlett, a marine biologist at the Scripps Institution of Oceanography in San Diego, California. "He's not going to have that much bottom time. So it's just not worth it" to deploy the lander.

Cameron—best known for creating fictional worlds on film (Avatar, Titanic, The Abyss)—remained optimistic.

"Next dive," he said. "Gotta leave something for the next one."

Speaking last week, Scripps's Bartlett had emphasized that Monday's dive was only the beginning and could "represent a turning point in how we approach ocean science.

"I absolutely think that what you're seeing is the start of a program, not just one grand expedition."

"The Ultimate Test"

Retired U.S. Navy Capt. Don Walsh, who descended to Challenger Deep with Swiss engineer Jacques Piccard in 1960, said he was pleased when he heard that Cameron had reached Challenger Deep safely.

"That was a grand moment, to welcome him to the club," Walsh, said in a telephone interview from the Mermaid Sapphire.

Walsh was one of the first people to greet Cameron as he climbed out of the sub.

Cameron told Walsh that Challenger Deep "hasn't changed a bit since you were down there.

"I felt a real kinship with you and Jacques on the descent, thinking, Man, this is a long way down ... It's crazy," said Cameron, a National Geographic Society explorer-in-residence.

On descent and ascent, the sub was "screaming down, and then screaming back up," Cameron said. We took off so fast from the bottom the whole thing was just shaking."

Expedition physician Joe MacInnis called Cameron's successful descent today "the ultimate test of a man and his machine."

Medical, Psychological Rigors

As the 57-year-old explorer emerged from the sub's coffin-tight 43-inch-wide (109-centimeter-wide) cockpit, a medical team stood at the ready.

But if recent test dives—including one to more than five miles (eight kilometers meters) down—are any indication, Cameron should be physically fine, despite having been unable to extend his arms and legs for hours, MacInnis told National Geographic News before the dive.

"Jim is going to be a little bit stiff and sore from the cramped position, but he's in really good shape for his age, so I don't expect any problems at all," said MacInnis, a long-time Cameron friend.

In addition, the sub's pilot sphere has a handlebar, which Cameron could use to pull himself occasionally up during the dive. "Usually, shifting position is all that's required to buy yourself another few hours," he said.

Because Cameron had prepared extensively for the dive, he should be in good psychological health, said Walter Sipes, an aeronautics psychologist at NASA's Johnson Space Center.

"He's got prior experience doing this, not just in the simulator but also training dives ... and he's an adventurer, so I really don't think they'll have any issues to worry about," said Sipes, who is not part of the expedition.

Still, if Cameron plans to conduct more dives—which the team has indicated he will—Sipes recommends he get plenty of rest in between or risk mental fatigue.

"When you start to get fatigued, you start making mistakes," he added. "And since he's down there solo, he can't afford that. He's a [potential] single-point failure."

It should be at least a few weeks before any further DEEPSEA CHALLENGE dives, as the director's next breakneck mission will take him from the middle of the Pacific to London, where he's due at a premiere of his Titanic 3-D Wednesday.

Cameron a Real-World Avatar

By returning humans to the so-called hadal zone—the ocean's deepest level, below 20,000 feet (6,000 meters)—the Challenger Deep expedition may represent a renaissance in deep-sea exploration.

While remotely operated vehicles, or ROVs, are much less expensive than manned subs, "the critical thing is to be able to take the human mind down into that environment," expedition member Patricia Fryer said, "to be able to turn your head and look around to see what the relationships are between organisms in a community and to see how they're behaving—to turn off all the lights and just sit there and watch and not frighten the animals, so that they behave normally.

"That is almost impossible to do with an ROV," said Fryer, a marine geologist at the Hawai'i Institute of Geophysics & Planetology.

Andy Bowen, project manager and principal developer of the Nereus, an ROV that explored Challenger Deep in 2009, said a manned mission also has the potential to inspire public imagination in a way a robot can't.

"It's difficult to anthropomorphize machines in a way that engages everyone's imagination—not in the same way that having boots on the ground, so to speak, can do," said Bowen, who's not an expedition member.

Biological oceanographer Lisa Levin, also at Scripps, said that the DEEPSEA CHALLENGE program's potential for generating public interest in deep-ocean science is as important as any new species Cameron might have discovered.

"I consider Cameron to be doing for the trenches what Jacques Cousteau did for the ocean many decades ago," said Levin, who's part of the team but did not participate in the seagoing expedition.

At a time of fast-shrinking funds for undersea research, "what scientists need is the public support to be able to continue exploration and research of the deep ocean," Levin said.

Perhaps referring to his friend's most recent movie, expedition physician MacInnis called Cameron a real-world "avatar."

"He's down there on behalf of everybody else on this planet," he said. "There are seven billion people who can't go, and he can. And he's aware of that."