How to mine the bottom of the sea.

The Atlantic goes deep, deeper than ever in search of the wealth beneath the ocean floor:

Today, many of the largest mineral corporations in the world have launched underwater mining programs. On the west coast of Africa, the De Beers Group is using a fleet of specialized ships to drag machinery across the seabed in search of diamonds. In 2018, those ships extracted 1.4 million carats from the coastal waters of Namibia; in 2019, De Beers commissioned a new ship that will scrape the bottom twice as quickly as any other vessel. Another company, Nautilus Minerals, is working in the territorial waters of Papua New Guinea to shatter a field of underwater hot springs lined with precious metals, while Japan and South Korea have embarked on national projects to exploit their own offshore deposits. But the biggest prize for mining companies will be access to international waters, which cover more than half of the global seafloor and contain more valuable minerals than all the continents combined.

Their collection vehicles will creep across the bottom in systematic rows, scraping through the top five inches of the ocean floor. Ships above will draw thousands of pounds of sediment through a hose to the surface, remove the metallic objects, known as polymetallic nodules, and then flush the rest back into the water. Some of that slurry will contain toxins such as mercury and lead, which could poison the surrounding ocean for hundreds of miles. The rest will drift in the current until it settles in nearby ecosystems. An early study by the Royal Swedish Academy of Sciences predicted that each mining ship will release about 2 million cubic feet of discharge every day, enough to fill a freight train that is 16 miles long. The authors called this “a conservative estimate,” since other projections had been three times as high. By any measure, they concluded, “a very large area will be blanketed by sediment to such an extent that many animals will not be able to cope with the impact and whole communities will be severely affected by the loss of individuals and species.”

Closest to the surface is the “sunlight zone,” where plants thrive; then comes the “twilight zone,” where darkness falls; next is the “midnight zone,” where some creatures generate their own light; and then there’s a frozen flatland known simply as “the abyss.” Oceanographers have visited these layers in submersible vehicles for half a century, but the final layer is difficult to reach. It is known as the “hadal zone,” in reference to Hades, the ancient Greek god of the underworld, and it includes any water that is at least 6,000 meters below the surface—or, in a more Vernian formulation, that is 20,000 feet under the sea. Because the hadal zone is so deep, it is usually associated with ocean trenches, but several deepwater plains have sections that cross into hadal depth.

Deepwater plains are also home to the polymetallic nodules that explorers first discovered a century and a half ago. Mineral companies believe that nodules will be easier to mine than other seabed deposits. To remove the metal from a hydrothermal vent or an underwater mountain, they will have to shatter rock in a manner similar to land-based extraction. Nodules are isolated chunks of rocks on the seabed that typically range from the size of a golf ball to that of a grapefruit, so they can be lifted from the sediment with relative ease. Nodules also contain a distinct combination of minerals. While vents and ridges are flecked with precious metal, such as silver and gold, the primary metals in nodules are copper, manganese, nickel, and cobalt—crucial materials in modern batteries. As iPhones and laptops and electric vehicles spike demand for those metals, many people believe that nodules are the best way to migrate from fossil fuels to battery power.

The ISA has issued more mining licenses for nodules than for any other seabed deposit. Most of these licenses authorize contractors to exploit a single deepwater plain. Known as the Clarion-Clipperton Zone, or CCZ, it extends across 1.7 million square miles between Hawaii and Mexico—wider than the continental United States. When the Mining Code is approved, more than a dozen companies will accelerate their explorations in the CCZ to industrial-scale extraction.

“I would be shocked if there aren’t vents and seeps in the trenches,” [Timothy Shank, of the Woods Hole Oceanographic Institution,] told me as we bobbed on the water that day in 2016. “They’ll be there, and they will be teeming with life. I think we’ll be looking at hundreds or thousands of species we haven’t seen before, and some of them are going to be huge.” He pictured the hadal as an alien world that followed its own evolutionary course, the unimaginable pressure creating a menagerie of inconceivable beasts. “My time is running out to find them,” he said. “Maybe my legacy will be to push things forward so that somebody else can. We have a third of our ocean that we still can’t explore. It’s embarrassing. It’s pathetic.”