IT IS a sobering fact that more people have walked on the moon's surface than have visited Earth's lowest spot. During six Apollo missions between 1969 and 1972, 12 humans did the moonwalk. Just two have plumbed Earth's ultimate depth. Their names are Jacques Piccard and Don Walsh, and their expedition to the Challenger Deep - the deepest point of the Mariana trench, some 11,000 metres below the surface of the Pacific Ocean near the island of Guam - lies over 50 years back, in January 1960.
The immense pressures and extreme cold of the ocean deep make reaching it a technologically demanding business. But sending humans into space isn't exactly easy. The discrepancy is largely down to politics: while the space race was fuelled by the rivalries of the cold war, no such spur has ever existed to encourage exploration of our oceans.
With the will to fund such ventures from the public purse on the wane, at least in the US and Europe, various private initiatives claim to be poised to take over the baton in the space race. Meanwhile something is stirring in the oceans too. The US film-maker James Cameron plans to send a crewed submersible into the Mariana trench to film footage for his follow-up to the film Avatar. And earlier this year, the British entrepreneur Richard Branson launched his one-person Virgin Oceanic submarine with the goal of visiting the deepest points of all of Earth's five oceans, the Challenger Deep included (see diagram). It is currently doing training runs with a view to performing the first full dives before the end of the year.
Branson is famous for his ability to attract publicity with well-funded, well-branded derring-do. "I didn't really understand why the oceans weren't being explored - it seems crazy when you think about it," he says. But this isn't just a Jules Verne-style yarn. A cadre of researchers have signed up to the project, and they have a long list of questions they want answered, from the ecology of deep-sea trenches to the role of trenches in Earth's geology. Is the light of science finally about to shine on our planet's deepest places?
The last time humanity made it down into the Mariana trench, it was ensconced in a contraption a little like a hot-air balloon in reverse. Piccard and Walsh's US navy submersible, Trieste, sank under its own weight into the trench and then discarded tonnes of iron shot to float back up. It spent 20 minutes at the bottom of the Challenger Deep, during which time the pair ate chocolate bars and looked out of the window. As they did so, they saw a shrimp-like creature float by in the inky blackness - a first proof that life could survive in a world with pressures well over 1000 times those at sea level.
In 1995, Japan's uncrewed Kaiko submersible provided further tantalising evidence of life down there in the shape of photographs of a worm, a sea cucumber and some shrimp. In May 2009, the uncrewed Nereus submersible, operated by researchers at the Woods Hole Oceanographic Institution in Massachusetts, collected liquid and rock samples from the bottom. And that's it - the sum total of humankind's interactions with the ocean's deepest depths.
The Mariana trench is a narrow scar in Earth's surface some 2500 kilometres long and averaging 70 kilometres wide. It began to form by the process of subduction some 50 million years ago, as the Pacific tectonic plate began to dive under the smaller Mariana plate to the west. The trench's depth is such that the currents that shuffle organisms around the rest of the ocean floor do not penetrate to its bottom. That makes the Mariana, and other trenches like it, evolutionarily isolated.
Charles Darwin showed 150 years ago how a similar isolation led the fauna of the Galapagos Islands to take bizarre forms - tortoises that grew to huge sizes, for example - and created the subtle diversity of Darwin's finches, each perfectly adapted to its island niche. But islands are mostly hospitable places, and can be reached by flying organisms, spores and pollen. The crushing pressures, cold temperatures and utter darkness of the ocean trenches, meanwhile, make them lethal to most creatures.
That means life found there was probably present as the trenches first started to form, allowing it to slowly adapt to the changing environment. "It really makes us wonder whether there are lost worlds of microbial organisms down there," says Katrina Edwards, a marine biologist at the University of Southern California in Los Angeles who is working with the Virgin Oceanic team.
But studying the ecology of the deep ocean floor is not as simple as dropping a probe on a cable, trapping something and hauling it back up. Organisms that live so deep tend not to survive the journey to the surface. "The pressure change just kills a lot of them," says Edwards. Instead, she and her colleagues rely on expensive automated landers, which use water pumps, filters and lures to collect principally microbial life and analyse it in situ.
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Sateesh.smart
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