Strewn across the Pacific seabed lies a vast treasure worth thousands of billions of euros.
And it is there for the taking. It just needs to be scooped up. No drilling required.
The greyish-black, potato-sized rocks, known as "nodules", do not look very inspiring. But they are packed with minerals such as manganese, copper, nickel, cobalt, zinc and rare earths that are essential raw materials for the electronics industry and products such as solar cells.
The price of these metals has surged in recent years because global demand for them is growing and their supply from mining on land is becoming increasingly scarce. Demand for copper alone is projected to double over the next 20 years, with more than half of that rise coming from China and India.
The biggest undersea reserves are located in a 5 million square kilometre area known as the Clarion-Clipperton Zone in the eastern Pacific.
The problem is the nodules lie at depths of up to 6,000 metres, where the water pressure is enormous. It is pitch black and close to freezing down there and the seabed at such depths still holds as many mysteries to mankind, if not more, as the moon.
Only a tiny fraction of it has ever been explored. A UN official once likened the technical challenge of deep-sea mining to someone standing on top of a New York skyscraper on a windy day and trying to vacuum up marbles from the street far below with a long hose.
In fact, deep-sea mining is a tad more difficult than that. It will require large, remote-controlled machines capable of combing the seabed and collecting the rocks. Not to mention a system of transporting tonnes of rock to the surface.
"I think it may take up to 10 years before the collectors and their components have been so well developed and tested that they function reliably," says Carsten Rühlemann of Germany's Federal Institute for Geosciences and Natural Resources (BGR).
"The machines have to be able to work for a long time because they would take about a week to lower to the seabed and a week to raise again," says.
"So if they don't function properly it will be prohibitively expensive to fix them. It will take a while for this to be commercially viable."
But despite these difficulties, the prospect of profits and access to strategic raw materials is about to trigger an underwater gold rush.
Critics say the world is on the threshold of a new colonial era, a dash for precious minerals that could do irreversible damage to marine ecosystems.
The UN's international seabed authority (ISA), which manages sea-bed mining, has so far granted 17 licences to national organisations and companies to prospect for minerals and more are about to follow.
Licence holders include companies from China, India, South Korea, Japan, eastern Europe and Russia, Germany, France and the United Kingdom, as well as the Pacific island nations Kiribati and Tonga.
The potential for deep-sea mining is "arguably higher now than at any other time in history", the ISA said in a study released in February.
The race for minerals could lead to international tensions. The United States, which has not been allocated an exploration area because it never signed the UN convention on the law of the sea, is unlikely to stand by while others exploit the riches of the oceans, especially since the most lucrative areas are close to the western coast of the US and Mexico.
The ISA, therefore, will have to rise to a huge challenge. So far, its role has largely been confined to handling bids for mineral exploration. Now, it has to work out how to licence, regulate and monitor the first real seabed-mining operations and how to share the proceeds.
It proposes to provide operators with "provisional mining licences" to make sure they demonstrate real mining and environmental competence before they are granted a full licence.
"Deep ocean mining is faced with a 'Catch-22' situation, whereby competence cannot be gained without actual mining at a commercial scale but, at the same time, mining should not be allowed without prior demonstration of competence," the ISA says.
According to its study, the Clarion-Clipperton Zone may have more than 27 billion tonnes of nodules containing seven billion tonnes of manganese, 340 million tonnes of nickel, 290 million tonnes of copper and 78 million tonnes of cobalt.
How much of that is actually accessible is unknown, however.
"The technology hasn't been properly developed for use on an industrial scale although the Koreans, Indians and Chinese have made progress with test collectors," says Mr Rühlemann, the BGR's expedition leader on a German-French research trip to the Pacific last year to assess the possible environmental impact of mining. South Korea has already undertaken 30 exploratory missions to its licence area in the Pacific and has set up its own test site for automatic deep-sea mining vehicles. Last year the Jiaolong, a Chinese manned deep-sea research submarine capable of navigating horizontally along the seabed, dived to a depth of more than 7,000 metres.
Aker Wirth, a German mining technology company, has drafted a design for a 17-metre long, 250-tonne machine resembling a combine harvester that would move across the seabed on several tracks.
At the front, cylindrical drums with little shovels would scoop up the nodules and feed them into a machine where they would be ground up. An enormous pump would bring them to the surface with the help of compressed air.
A major boost to deep-sea mining came from Papua New Guinea granting the first deep-seabed mining licence to the Nautilus Mining Company of Canada, in its territorial Bismarck Sea. The deal showed the private sector, and the banks supporting it, that deep-seabed mining is now commercially feasible.
Nautilus planned to mine for copper and gold on the seabed, not from nodules but from so-called "massive sulphide deposits" emitted from hydrothermal vents in the ocean floor where superheated water carrying metals from deep in the earth mixes with cold seawater to form metal-rich deposits.
However, that project, due to start production this year, is currently on hold due to a legal dispute with the government of Papua New Guinea.
Biologists argue seabed mining of nodules will harm the environment by churning up underwater clouds of sediment and displacing deep sea creatures. The operations could wipe out unique species before they had even been discovered, they say.
"Collecting manganese nodules will plough up a few thousand square kilometres per year. That would have similar consequences as cutting down rainforest," says Sven Petersen, a scientist at the Helmholtz Centre for Ocean Research in Kiel, northern Germany.
"It's not as though no animals or plants live there afterwards. But they're completely different species. And it's exactly the same with deep-sea mining." Jon Copley, a biologist from the University of Southampton, says it is a joint task to look after the oceans.
"I don't think we own the deep ocean in the sense that we can do what we like with it. Instead, we share responsibility for its stewardship," he told the BBC.
"We don't have a good track record of achieving balance anywhere else - think of the buffalo and the rainforest - so the question is, can we get it right?"
Mr Rühlemann says the environmental damage from so-called suspension clouds churned up by the mining vehicles may be less severe than feared.
"I don't think suspension clouds will drift far because the currents are very slow at such depths, just 3 to 4 centimetres per second," he says.
"Besides, fine-grain sediments tend to clump together quickly and sink back down to the floor.
"The collectors will squash things but due to their wide chassis the pressure on the seabed would be kept to around 200 grams per square centimetre, which is about the same as a human being standing on the seabed."
But the true impact won't be known until large machines are used, he sadds.
"You'd have to put a machine down there and monitor what actually happens when it moves. Nobody's done that yet."
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