People have been clawing valuable minerals like iron and gold out of the ground for millennia. And for much of the stuff that touches our lives today—from the europium, terbium and yttrium that help illuminate the screen you are reading to the copper in the wires that power it—we increasingly depend on elements from the depths of the Earth. But finding new deposits gets harder every year and mines are steadily growing larger, more expensive and more environmentally destructive.

On land, that is. By some estimates the ocean floor has the planet’s largest resources of minerals such as copper, nickel and cobalt. The deep sea also holds gold, silver, platinum and the rare earth elements used in high-tech devices and renewable-energy technology including iPhone displays, solar panels and magnets used in hybrid cars. Underwater deposits often have much higher grades of ore than those on land, meaning they contain a higher percentage of the desired minerals—in some cases by an order of magnitude or more. The trick is getting the stuff to the surface in a cost-effective way.

Canadian mining firm Nautilus Minerals says it plans to lead the way with the world’s first commercial deep-sea mining project, scheduled to get underway within the next few years off the coast of Papua New Guinea.

The idea of mining the seafloor goes back at least to 1870when Captain Nemo in Jules Verne’s novel 20,000 Leagues under the Sea declared, “In the depths of the ocean, there are mines of zinc, iron, silver and gold that would be quite easy to exploit.” Only recently has deep-sea mining become technologically and financially feasible, thanks to using remotely operated subs and other technologies developed for deepwater oil and gas production. Proponents say higher ore grades mean deep-sea mining would be more cost-effective than land-based operations, with a smaller ecological footprint that would be less visible.

But these are uncharted waters, says Cindy van Dover, director of the Duke University Marine Laboratory in Beaufort, N.C. “We do not know where the tipping points are with regard to how much damage deep-sea systems can sustain and still maintain the health of the ocean,” she says.

SUNKEN TREASURES

Like deep-sea life, mineral deposits take strange forms on the ocean floor. Ferromanganese crusts form on the peaks and sides of underwater mountains, growing as slowly as one millimeter every million years. Polymetallic nodules that range in size from microscopic flecks to basketball-size blobs are rich in nickel, copper, cobalt and manganese. These rock concretions often lie scattered across the abyssal plains in most oceans.

In economic terms the most promising underwater resources are seafloor massive sulfide deposits. These form near hydrothermal vents when mineral-rich fluids heated deep inside Earth well up and hit cold seawater. The sudden cooling makes them deposit their suspended solids in the formations like chimneys that can reach about 45 meters high. Seafloor massive sulfide deposits typically occur between 1,500 and 4,500 meters deep along volcanically active ocean ridges and can contain high-grade gold, silver, copper, zinc and manganese.

One likely test case is Nautilus’s Solwara 1 Project, which will target a massive sulfide deposit 1,500 meters deep in the Bismarck Sea northeast of New Guinea. Nautilus estimates the site could produce more than 72,500 metric tons of copper and more than 4.5 metric tons of gold. The copper ore grade—the concentration of a valuable mineral within an ore—averages nearly 8 percent, compared with 0.6 percent on land in 2015, says Nautilus chief executive Mike Johnston.

To collect this treasure Nautilus has designed a trio of huge, remote-controlled underwater machines that would not look out of place in a Terminator movie. Two “cutters”—weighing 308 and 250 metric tons, respectively—will crawl across the seafloor on tank treads and grind the ore into slurry using spinning toothed wheels. A 2,200-metric-ton collecting machine will feed the slurry into an enclosed pumping system to the surface. Operators in a support vessel control the cutters and collecting machine using joysticks, sonar and live streaming video. Onboard the support vessel the slurry will be drained and transferred to another ship for processing in China. The wastewater will be filtered of impurities and pumped back down to the seafloor.

AQUATIC ECOSYSTEM IMPACT

Johnston says the entire project has been designed to minimize impact, with no tailings (ore from which minerals have been removed) left behind at the site. “On the seafloor you don’t have to mine down a whole mountain, compared to an open-pit mine where you might have three tons of waste for every ton of ore,” he says. The project planning has involved independent reviews and environmental impact studies with help from experts at the Woods Hole Oceanographic Institution in Massachusetts, the Scripps Institution of Oceanography in California and others. Whatever effect the mining has, the site should fully recover within five to 10 years after the project is finished, according to Johnston.

Richard Steiner, a conservation biologist and former University of Alaska professor who is not involved in the Solwara project, is unconvinced. “There’s no question this will pose massive environmental impacts,” he says—from bright lights, noise and potential toxic leaks to sediment plumes that could clog the filters many kinds of sea life use for feeding. The deep ocean is the largest and least understood biological habitat on Earth and deep-sea vents—discovered as recently as 1977—may be one of the rarest of all ecosystems, says Steiner, who heads up the conservation consultancy Oasis Earth. Only about 300 vent sites are known and estimates of the total number that exists range between 500 and 5,000.

Impact reports that use land-based mines as a benchmark are comparing apples and oranges, Steiner says—and our environmental track record in deepwater oil and gas recovery is not exactly inspiring. The deep ocean is unforgiving, even to experts; in 2014 Woods Hole’s Nereus robotic sub imploded in the Kermadec Trench, a 10-kilometer-deep rut in the Pacific Ocean floor where two tectonic plates meet northeast of New Zealand. “There’s a dangerous combination of ignorance, arrogance, greed and very poor scientific understanding,” Steiner says. “Humans are terrestrial primates; we just don’t get underwater.”

The Solwara project will answer some of these questions, assuming Nautilus team carefully monitors its operations and shares the information with scientists and the public as promised, Van Dover says. That is still a big “if”. Nautilus initially planned to start testing operations in early 2018 but funding issues have pushed the date back indefinitely until the company can find a way to pay for the project. Meanwhile researchers have discovered high-grade gold at a hydrothermal deposit south of Tokyo. Further, China is testing deep-sea mining exploration vehicles and has announced plans to build an underwater lab to hunt for minerals in the South China Sea. The International Seabed Authority, which governs deep-sea mining in international waters, has already approved 27 exploration plans to take place over the next several years in oceans around the world.