There in the mud, just waiting to be scooped up, is a natural resource deposit potentially worth billions and billions of dollars. It contains chemical elements needed by automakers, by manufacturers of consumer electronics and by green technology developers—elements for which China currently holds a global near monopoly.

The catch? The mud, which is enriched in the technologically crucial metals known as the rare earth elements, is beneath thousands of meters of water in the Pacific Ocean. Extracting resources from such depths brings technological, economic and regulatory hurdles, all of which would have to be overcome before deep-sea rare earths become an ingredient in tomorrow's catalytic converters, wind turbines and computer screens. As a result, experts say, it will be many years—if ever—before that seafloor resource is tapped.

The deep-sea rare earths came to light in a study by a group of Japanese researchers, which was published online July 3 in Nature Geoscience. (Scientific American is part of Nature Publishing Group.) The researchers analyzed more than 2,000 samples of Pacific seafloor sediment and found high concentrations of rare earth elements. (The 17 rare earth elements include the lanthanide series—from lanthanum to lutetium on the periodic table—plus yttrium and scandium.) They estimated that there could be more than 100 million metric tons of rare earth compounds in the seafloor mud. And a preliminary estimate showed that one square kilometer of seafloor mud around a sampling location known as site 1222 could provide one fifth of the world's annual supply of rare earths. But the reality is that extracting that mud is not yet feasible for a number of reasons.

"To characterize it as something that's an economic resource might be an overstatement at this point," says Porter Hoagland, a senior research specialist in marine policy at the Woods Hole Oceanographic Institution (WHOI). "There are a host of economic factors that kind of work against a cost-effective recovery offshore."

To access the rare earths at site 1222, for instance, would require pulling up the top 70 meters of seafloor sediment, filtering out the water content, removing the valuable rare earths (which make up less than one part per thousand of the sediment) and returning the rest of the material to the seabed.

Such an undertaking would require new technology, a long permitting process—and, of course, a lot of money. So there would have to be a significant economic incentive to access the seafloor resource. "That's why I'm not sure the rare earth elements are enough in themselves to provide that," says James Hein, a geologist at the U.S. Geological Survey in Menlo Park, Calif. After all, the global rare earth market is relatively small—it currently runs about $2 billion to $3 billion annually, according to a recent report from Ernst & Young, whereas the markets for metals such as copper are dozens of times larger. "I'll be surprised, really, if this gets much attention as a resource potential in the near term," Hein says. "The grades really are just not very high, and the environmental issues will just be so great."

At depths of 4,000 to 5,000 meters, seafloor ecosystems are not well understood, nor are the potential impacts of large-scale dredging on those ecosystems. "Essentially, this would be a strip-mining operation where they would be sucking up lots of sediments from the seafloor over large areas," says Craig Smith, a professor of oceanography at the University of Hawaii at Manoa, "which would of course destroy the communities that reside there." Those ecosystems, to the extent that they have been explored, have low biomass but high biodiversity. And, having taken hold in a stable environment, they are not adapted to large-scale disturbances.

"Four thousand meters in the deep ocean is a long way down, and we don't know how to mitigate against significant environmental impacts or how to restore the ecosystem, if you can even restore the ecosystem," says Cindy Van Dover, an oceanographer at Duke University. "We don't understand a lot about what is going on down there from an ecological standpoint."

Many of the sites sampled by the Japanese researchers are in international waters and would fall under the jurisdiction of the International Seabed Authority, based in Jamaica, which means any mining concern looking to extract seafloor rare earths would likely face a long regulatory process. "Doing things there is a very slow and considered process," Van Dover says. "Things don't happen overnight in international waters."

If it does become economically feasible to extract rare earths from the Pacific seafloor, the needs of ecosystems on the seafloor will have to be balanced with the economic and societal benefits from mining there. Rare earths appear in a number of products in relatively small quantities—as phosphors in plasma screens, for instance. Much larger quantities are needed for some green-technology applications—the batteries in hybrid cars contain several kilograms of rare earths, and the magnets used in wind turbines can require hundreds of kilograms.

"If the human demand for metals continues to be as high as it is, or go up, then there will be continued demand for these metals and rare earth elements," Smith says, adding that involving marine scientists early on can help ensure that exploitation is carried out in a responsible way. "I personally would prefer not to see the deep sea trashed, but I think we have to be realistic," he says.

For the time being, though, the barriers to extracting rare earths from the seafloor loom large. And if the deep-ocean mud is never tapped, it would not be the first time that seafloor resources have been trumpeted without much follow through from industry. "My skepticism comes from years of grandiose claims and then nothing really happening," WHOI's Hoagland says. "That says to me that it's not cost-effective to go get this stuff."