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Conditions this extreme would kill any land animal in an instant, but vents teem with creatures who have never seen the sun. They thrive on chemosynthesis—chemical energy—rather than light energy from photosynthesis. Back in 1977, when hydrothermal vents were first discovered on the Pacific seafloor, no one had any idea that such an otherworldly ecosystem could exist here on earth. Now it’s clear that life has more tricks up her sleeve than we’d known, and the deep ocean is where she performs them—on this planet, and potentially others. (If we find life on Saturn’s ocean moon Enceladus, as scientists believe is a real possibility, it will likely reside at a chemosynthetic vent.)

Could anything be more thrilling? I’ve always been obsessed by the idea that beneath the waves there’s a vast kingdom filled with places we’ve never seen, creatures we’ve never met, wonders we’ve never imagined. Yet even as we’ve charted Mars down to its individual craters, only 25 per cent of the earth’s seafloor has been mapped at high resolution. Millions of submarine volcanoes, mountains, rift valleys, canyons, craters, plains, vent fields: all unknown to us. We’ve explored less than 0.1 per cent of the deep ocean.

This is no small omission. The deep ranges from 200 metres to 11,000 metres down and occupies 95 per cent of our biosphere. It isn’t just a part of our planet—it is our planet. It’s the engine that drives climate, ocean currents, heat circulation, and biogeochemical cycles. It sequesters our carbon dioxide and gulps down the excess heat we’ve generated from burning fossil fuels. And unlike space, every last bit of the deep is alive. It’s a cosmos of creatures, a galaxy of microbes, a reservoir of genomic innovation that has kept life going for eons. A list of the services the deep ocean provides, and that we take for granted, would stretch for miles and include this one: making it possible for us to survive on this spinning rock. This realm is obscure, uncharted, and urgently important if we hope to stick around. If we’re to have any chance at turning back the tide on climate change, or our self-inflicted sixth global mass extinction. If we have any interest in learning about its marvels, finding next-generation medicines, understanding earth systems, or unravelling the origins of life. The deep ocean is our greatest mystery and our greatest hope. That’s why it’s so completely insane that people are now rushing to strip-mine it.

In the history of bad ideas, deep-sea mining is one for the Hall of Fame. While it hasn’t yet begun on an industrial scale, dredging the seabed for metals has long been a gleam in the corporate eye. In swaths of the ocean’s abyssal zone, from 3000 metres to 6000 metres down, the seafloor is carpeted with polymetallic nodules: nuggets that contain manganese, nickel, cobalt, and traces of copper. They precipitate from the seawater over tens of millions of years, aided by microbes in an alchemy that we can’t explain. Animals and other organisms live on, under, and even inside the nodules, which are habitats like trees in a forest or corals on a reef, albeit far more ancient—and their infinitesimally slow growth means that once they’re removed, they’re not coming back. These odd little orbs form a living layer of the seafloor that has survived, untouched, since the Mesozoic era.

Deep-sea mining’s boosters will tell you that we desperately need seabed metals to build batteries for a “greener” high-tech future, but we don’t. There’s already a global oversupply of manganese; the latest battery chemistries don’t require any cobalt or nickel. Nevertheless—although some deep-sea mining plans call for scalping the tops off seamounts or gouging out hydrothermal vents—the most aggressive players are fixated on the nodules.

Their first target is the Pacific’s Clarion-Clipperton Zone (CCZ), a 4.5 million-square-kilometre (yes, you read that right) tract of seafloor on the high seas that stretches from Mexico to Hawaii. Although the miners refer to the CCZ as a “lifeless desert,” researchers racing to study the area before it’s annihilated have found the opposite to be true. The CCZ is one of the deep’s most spectacularly biodiverse regions, precisely because it’s so densely packed with nodules: deep-sea creatures co-exist symbiotically with them. Far from a wasteland, the CCZ is a cabinet of curiosities. During sampling expeditions, an estimated 90 per cent of the animals collected there have been new species.

“In terrestrial environments it’s really remarkable if you find an animal, especially a larger animal, that’s new to science,” oceanographer Craig Smith, the leading expert on the region, told me. “In the CCZ in particular, every box core we take, every sediment sample we take—we have hundreds of species that haven’t been described.”

In case you’re wondering if any of these dazzling new species will be spared when the mining machines grind through the CCZ—the answer is no. Everything will be razed: think clear-cutting a forest while also sucking up the topsoil. (By the way, deep-sea sediments are also alive and contain ancient microbial networks.) “I don’t think there’s any reasonable expectation that any life that exists in the [direct mining] area will survive,” MIT oceanographer Tom Peacock concluded in a 2019 TED Talk. “That will be lost.”

The ocean's abyssal zone is the biggest, most powerful protector we’ve got: it swaddles the earth like a blanket. Keeping this refuge in balance would seem like an important enough job, but that’s not the nodules’ only function. New research indicates that these odd little orbs play a previously unknown role in the ocean’s geochemistry. By generating an electrochemical reaction on their surfaces, the nodules appear to be emitting a one-volt charge that splits seawater into hydrogen and oxygen, creating what scientists refer to as “dark oxygen.”

Another oxygen source on earth… that seems like something we might not want to wreck. Perhaps a little humility is in order? Hubris is always the opening act for failure, and here is its ultimate expression: sending 100-ton machines down through three miles of saltwater to claw into the ocean’s womb so that we can make more cell phone batteries. No extractive industry is eco-friendly, but deep-sea mining stands alone in its potential for havoc because its footprint will be so massive, its damage will be irreversible on human time scales—and we won’t even know what we’ve destroyed. As the renowned oceanographer Sylvia Earle puts it: “I mean, come on—these are the very systems that are keeping us alive. The deep sea has kept us relatively safe. We should leave it the hell alone.”

Because, truly, it’s time to stop damaging our mothership and start repairing it. Less exploitation, more exploration. Less negligence, more reverence. The ocean is resilient: it will heal if we let it. Astronauts talk about the overview effect, a transcendent mind-shift that comes from gazing down at earth, so preposterously lush with beauty and life, floating in the vast cosmic darkness—and being overcome by awe, and a fierce desire to protect it. Diving into the abyss, I’ve learned there’s an underview effect, too. It’s a deep feeling of peace, a longing to come into harmony with the ocean that sustains us. And in doing so, to at last know the majesty of our own home.

Susan Casey’s most recent book is The Underworld: Journeys to the Depths of the Ocean

This story features in Roaring Journals Edition Three: order your magazine here.