For two and a half hours, she strolled slowly through this otherworldly environment. As her dive concluded, she reboarded the submersible for the return ascent, her mind awash with what she had observed. On reaching the surface, though, her own thoughts were drowned out by questions from her colleagues: What had she seen? How had the equipment worked? What was life like at the bottom of the ocean?

“I was delighted that people wanted to listen, and tried every way I knew how to explain not only how beautiful it is in the deep sea, but also, how urgent it is for us to understand as much as possible about the nature of the complex ocean systems that occupy so much of Earth,” Earle later wrote.

Earle had long lamented the consequences of one-sided engagement with the sea and its inhabitants. Divers, she knew, were often “grim ambassadors” of the human race.

Jacques-Yves Cousteau, the pioneering scuba diver whose undersea narration beckoned her into the deep, dynamited coral reefs to study dead fish. His crew killed sharks with harpoons and axes, decrying them as divers’ “enemy,” and hunted with spears for both sustenance and sport. In the second half of the 20th century, the development of diving technology, including the pressurized suit Earle wore that historic day, was largely driven by the needs of an expanding and increasingly destructive offshore oil and gas industry.

Forty-five years later, the situation is dire. The oceans are acidifying, marine species are depleted, and dead zones are proliferating. Governments and multinationals are turning to deep-sea mining to supply new technologies to feed our ravenous energy demands, with the oceans’ health in the balance.

Earle’s reflections on the scuba equipment that first brought her beneath the surface as a teenager carry the heavy weight of hindsight, mourning the unintended consequences that accompany so much of the history of diving.

“Technology that for the first time provided effective access, the key to understanding the sea, perversely made possible its accelerated destruction,” she wrote.

Bounty Beneath the Surface 

The ocean and its bounty drew people into the seas long before technology gave them the tools to dive deep and stay there. Ancient civilizations around the Mediterranean gathered precious red coral for jewelry, mother-of-pearl for carved ornaments, and shellfish for imperial purple dye. Sponges were collected for bathing, medical care, and decoration. Pearls and the divers who could secure them were prized everywhere from India and present-day Sri Lanka to Japan. 

For most of human history the work of surfacing these resources was done without aid, but even the most skilled free divers can only make it down a few hundred feet—and then for just a few moments. Every 33 feet of depth adds another atmosphere of pressure on the body, 14.7 pounds per square inch, an unavoidable antagonist.

To overcome the sea’s defenses, determined divers brought the world above the waves down with them. In the 4th century BCE Aristotle described seeing sponge divers use “a kettle . . . not filled with water, but with air, which constantly assists the submerged man.” Among the many stories told of his pupil Alexander the Great is one in which Alexander is lowered in a great glass diving bell, bent on conquering the sea.

More definitive in the historical record is Italian inventor Guglielmo de Lorena’s 1535 design of a piece of equipment to explore the remnants of a barge, built as a floating palace for Emperor Caligula, that had sunk just below the surface of Lake Nemi in the 1st century CE. De Lorena’s creation was relatively simple: an oak barrel secured with iron hoops and “caulked and greased like a ship,” which he wore over his head and torso as he walked along the barge, 10 meters down.

The usefulness of early bells was limited, though, by the crushing weight of the sea. As a diver went deeper, the air trapped inside was compressed further, shrinking the breathable space. That made the device functional only within close reach of the surface. Working conditions were also hazardous, owing to the accumulation of carbon dioxide in the bell’s interior and the limited amount of breathable oxygen.

Making the most of the diving bell would require a steadier supply of air, a feat that Edmond Halley, the English astronomer and physicist, attempted to tackle in 1716’s “The Art of Living Under Water.” He described a lead-covered wooden bell with 60 cubic feet of space inside, enough to comfortably hold two divers who could breathe through a tube connected to two lead casks submerged alongside the bell.

Though Halley couldn’t solve the pressure problem of the deep, which caused pain “as if a quill were forcibly thrust into the hole of the ear,” his blueprint still traveled far and wide. His casks remained the primary tool for underwater enterprises through much of the 18th century, as salvage companies across Europe slipped past the sea’s surface in search of the continent’s sunken riches.

Squeezed and Bent

The Royal George was the world’s largest warship when it launched in 1756, a 2,000-ton, 108-gun behemoth. It was anchored near Portsmouth, England, with 1,300 sailors aboard in August 1782 when it suffered one of the worst maritime disasters of the 18th century. To repair a small leak below the waterline, its guns were gathered to one side to tilt the ship and expose the damage. As its creaking timbers sagged under the strain and sent it askew, the ship took on water and suddenly sank, taking some 900 lives with it. It came to rest upright, 65 feet down, its masts breaking the surface as a ghostly reminder.

The navy devised several schemes to remove the imposing obstacle and recover its remnants, but nothing worked, including excursions using a diving bell. For more than 50 years the Royal George sat rotting in the harbor, until, in the summer of 1840, a Prussian immigrant delivered a diving suit that became the state of the art.

Augustus Siebe modeled his creation on a helmet and jacket originally designed for entering smoke-filled buildings. It was a closed suit whose helmet of hardened copper and glass portholes could be quickly unscrewed from its breastplate, making dressing and undressing a breeze. The suit delivered compressed air to a diver by hand pumps and could be inflated to provide counterpressure against the sea. With minor modifications, it is still known as “standard dress” for divers, prized for the range of motion and security it affords.

Underwater, though, security is relative. As divers set about salvaging what they could from the Royal George’s hulk and demolishing it with gunpowder charges, one encountered a danger Siebe had not anticipated: “the squeeze.”

Private John Williams was in the midst of a dive when his air pipe broke and the pressure in his suit demanded release. He was struck motionless by the sudden shock and a feeling “as if he were being crushed to death,” according to his medical record. Workers hauled him to the surface, where he retched gore as blood flowed from his ears. It was the first documented case of such a disaster, and Williams was lucky to walk out of the hospital a month later, never to dive again.

Historian James Dugan later described the horror of the squeeze in grisly detail. “Sometimes the collapse is complete; the flesh is sucked off [the diver’s] bones and goes streaming up the pipe and the skeleton is jammed into the helmet.” A non-return valve was added to Siebe’s design in an effort to prevent further catastrophes.

The squeeze was among the more violent ways the sea punished divers’ incursions, but it certainly wasn’t the only one. As divers went deeper for salvage, civil engineering, and, eventually, science, the hazard that truly threatened them was not the descent but the ascent. Any diver who surfaced too quickly dealt with decompression sickness—known as “the bends” for its ability to “choke you to death, kill you instantly, or twist you into a screaming lump of agony with awful pains in your joints,” in the words of underwater archaeologist Peter Throckmorton.

English chemist Robert Boyle had unwittingly documented evidence of the bends beginning in the 1660s during a series of experiments to understand the pressure exerted by the air. He placed a viper into a bell jar, removed the air with a pump, and watched as the snake’s “body and neck grew prodigiously tumid, and a blister appeared upon the back.” In a similar experiment, he noticed that a “conspicuous bubble” had formed in a viper’s eye.

An explanation of the reaction’s cause—and its implications for ascending divers—waited for two centuries, until French physiologist Paul Bert published La pression barometrique in 1878. Through experiments on the rapid decompression of mice, dogs, and birds, Bert learned that “pressure acts on living beings not as a direct physical agent, but as a chemical agent.”

Air is mostly nitrogen (78%) and oxygen (21%), with a variety of trace gases making up the rest. Unlike other gases that are passed off in respiration, nitrogen is driven into solution in the body under pressure. Underwater, divers breathe more air to maintain their pressure against the sea—twice as much as at sea level at 33 feet down, three times as much at 66 feet, and so on—meaning that with each additional atmosphere a diver descends, more nitrogen enters the blood and tissue. So long as a diver maintains a consistent pressure, the nitrogen stays in solution, like the carbon dioxide in a corked bottle of champagne. But surfaced too quickly—pop!—the bubbles burst forth.

The glint Boyle saw in the viper’s eye was an embolism caused by this explosion of nitrogen. Likewise, the overflow of gas blocks divers’ blood vessels and throttles their nervous systems as they re-emerge. To prevent the bends, Bert said, divers could resurface slowly, allowing nitrogen to gradually pass out of their bodies. In the early 20th century, Scottish physiologist John Scott Haldane developed the first decompression tables—a guide for slow, stepped ascents that would keep divers from uncorking their bottles.

Nitrogen pestered divers in other ways. The gas’s infiltration of the body caused a kind of intoxication, known as nitrogen narcosis, that impeded divers’ work. Jacques Cousteau called it the “rapture of the deep.” Haldane’s son, physiologist J.B.S. Haldane, offered a fix, determining that the complications of breathing compressed air at depth could be avoided by using a helium-oxygen mixture rather than one dominated by nitrogen. His recipe is still preferred for dives beyond 400 feet. 

With tanks of compressed air filled with the right mix of gases, divers could finally evade the worst of the sea’s weapons. Soon, Cousteau’s development of a self-contained underwater breathing apparatus, or scuba, made diving widely accessible for the first time, breaking open the sea as the site of adventure, exploration, and scientific research.

Flying without Wings

Jacques Cousteau had wanted to be a pilot. His eyes were on the skies when he enrolled in the French naval academy between the world wars. But when he crashed his roadster while racing through the hairpin turns of the Vosges Mountains on the way to a friend’s wedding in 1935, his path was redirected. With bones broken throughout both arms, he took months to recover in the south of France, where painful daily swims in the Mediterranean aided his rehabilitation. After a friend gave him a pair of goggles to see beneath the surface, his future came into focus. He was shocked by the beauty he saw. “From that day on, all my free time would be devoted to underwater exploration,” he said.

The technology to dive deep without a connection to the surface didn’t yet exist, so Cousteau, a man so slender that a woman once asked if he had been shrunk by the sea’s pressure, became an inventor by necessity.

In 1943 he and engineer Émile Gagnan designed a demand valve that seamlessly delivered air from tanks carried on a diver’s back, whenever—and only when—the diver inhaled. With the Aqua-Lung, as they called it, underwater adventuring entered a new era. In 1953’s The Silent World, Cousteau wrote lyrically about swimming at record depths “with the freedom of fish.” He had wanted to be a pilot. Now, he wrote, “I flew without wings.”

If centuries’ worth of diving technology had given humans the tools to dip a toe into the oceans’ uppermost reaches, the Aqua-Lung allowed them to dive in with abandon. Swiss oceanographer Jacques Piccard wrote that it “sparked a mass invasion of the sea,” and Sylvia Earle was among those new entrants.

Earle had first fallen in love with the sea’s power at the edge of the cool Atlantic Ocean, on visits from her native Gibbstown, New Jersey, then moved as a child to Florida’s west coast, where she waded in the warm gulf waters. By the early 1950s, when the Aqua-Lung became commercially available, she was a botany major at Florida State University, still “irresistibly drawn” to the sea. Her marine biology professor thought the best way to study fish was to go where they were—an ethic she carried forward—and so she was among the first wave of users to dive with the Aqua-Lung and observe marine life in situ. Even on her first dive, though, she seems to have sensed the way humans disrupt the ocean’s equilibrium, encountering a tiny damselfish “who was not pleased by my intrusion into its territory.”

Earle continued to study botany at Duke University over the next decade, slowed but not deterred by having two children. She was invited on a series of extracurricular expeditions that took her to the Mediterranean, South Pacific, and Indian Ocean. Her doctoral dissertation—to which the international journal Phycologia devoted an entire issue—tracked the distribution and abundance of algae in the eastern Gulf of Mexico. Unlike earlier marine biologists, who had done their work with uprooted samples, she was able to describe firsthand the characteristics of 72 species of algae.

As astronauts blasted into outer space throughout the 1960s, Earle joined a generation of aquanauts descending into what she described as “inner space.” Using any means available—scuba gear, diving helmets, even a submersible whose lockout chamber allowed her to swim out at a depth of 100 feet (while four months pregnant, no less)—she entered the sea with the hope of better understanding it.

In 1969, the year Apollo 11 astronauts set foot on the moon, the U.S. Navy collaborated with NASA to launch an undersea station where divers could stay submerged not for mere hours, but for days and weeks. The potential of saturation diving—so-called because a diver’s body remains safely saturated with nitrogen as long as they remain at depth—was enormous for Earle and this new breed of marine scientists. If the best way to observe a fish was to become a fish, as Cousteau had written, living underwater offered an entirely new way to understand ocean life.

Earle, then focused on exploratory field research at Harvard University, was selected to join an all-female team that spent two weeks in the summer of 1970 in the station, named Tektite, a habitat 50 feet below the ocean’s surface in the Virgin Islands. Over the course of half-day dives down to 100 feet, she witnessed the enormous scope of marine life, learning to recognize individual fish among the many species whose habits she scrutinized, day and night. In an underwater laboratory, she observed that “details come into focus, relationships among the reef residents gradually become known, the subtleties that make a system really work become evident,” as she later wrote. For a botanist, so much time at depth was a “rare treasure.”

Such opportunities only became more scarce. Modest federal funding for ocean science dwindled over the ensuing decade, and most undersea habitats developed for scientific use were retired in short order. Saturation diving soon was relegated to commercial applications—namely, serving the needs of an expanding offshore oil and gas industry that had been born in the Gulf of Mexico not long before Earle was beginning to explore it.

The first commercial offshore oil well was drilled in 1947, surfacing petroleum through 14 feet of open water 10 miles off the southeastern coast of Louisiana. In the years that followed, demand for oil soared as the United States’ postwar economy surged, driven by a booming auto industry. Soon, the race for the resource that defined the 20th century spread far and wide—with divers playing a critical role in its development.

In 1954 Cousteau sailed to the Arabian Gulf on a former Royal Navy minesweeper he called Calypso. Two years earlier he had taken it to the Red Sea to study coral, but now he had been hired by British Petroleum, which owned the rights to any deposits off Abu Dhabi’s coasts, to retrieve rocks from the seabed that might contain evidence of oil lying in wait. Four years after his successful survey, a 4,000-ton floating rig built in Germany and dragged across four seas to reach the gulf drilled through 30-million-year-old limestone to find oil, nearly 9,000 feet below the water’s surface. In 1963 Abu Dhabi produced 44,000 barrels of offshore crude per day; today, it exceeds 4 million.

Cousteau’s relationship with the oil industry continued into the 1960s, when his Conshelf undersea habitat—a Tektite predecessor—showed that subsea stations could be used for oil exploration and recovery. Housed in a dwelling 328 feet below the surface of the Mediterranean off the southern coast of France, Cousteau’s divers used buoyancy to their advantage to attach a 400-pound repair assembly to a wellhead more quickly than could a crew on land. Their work was proof of concept; the industry took notice.

Through the 1970s, research-minded saturation diving projects gave way to those focused on oil. By the end of the decade even the frigid, wild waters of the North Sea had succumbed to the offshore rush. As offshore drilling spread around the world, divers supplied the underwater skill to keep rigs running. Offshore oil, in turn, supported most commercial diving work.

An Exotic Lab Coat

In his history of commercial oil-field diving, diver Nicholas Zinkowski wrote that the offshore oil industry is “almost solely responsible for the tremendous surge in diving activity and technology.” With investment in marine science lagging far behind space science, industry funding bolstered the development of technology from saturation diving stations to submersibles to remotely operated vehicles. The armored suit Earle used to make her record-setting dive off Oahu was among this menagerie.

Long before Earle stepped into her leaden boots, John Lethbridge, an English wool merchant, designed the first rudimentary armored diving suit in 1715—a sealed barrel with a glass window and holes through which his arms could dangle as he laid outstretched on his chest. With his barrel, he dove hundreds of times up to 60 feet and sometimes a bit further “with great difficulty,” recovering nearly 100,000 pounds of cargo from wrecks for European shipowners.

Guy Sechrist, a historian of science at the University of Tennessee who has studied early salvage diving, says Lethbridge lived into old age, his arms “completely mangled” from so many unprotected visits to and from the pressurized sea.

Two centuries after Lethbridge’s so-called “diving engine” first encased a diver, British engineer Joseph Peress, a Persian immigrant, picked up the torch. He had envisioned a diving suit for recovering pearls from the deep waters of the Persian Gulf, but after a decade of work his creation met a different purpose.

A prototype, built in 1923 and made entirely of stainless steel, could maintain an internal pressure of 1 atmosphere, equal to that on land, but the suit’s 3,000-pound weight nearly immobilized the diver. A second iteration, made of cast magnesium alloy, weighed a more modest 800 pounds. In 1935, diver Jim Jarrett used the suit, known as Tritonia, to locate the Lusitania—a British cruise liner famously sunk 20 years earlier by a German submarine—300 feet deep off the coast of Ireland. Despite its success, Tritonia didn’t immediately drum up much interest. The Royal Navy couldn’t envision sending divers quite so deep. The suit sat in storage until the 1960s, when oil companies were searching for ways to exploit the North Sea’s deep reservoirs.

By the time Earle suited up, in 1979, she was entering its ninth generation, modernized by the British engineer Graham Hawkes (her future husband) and now known as a JIM suit, in honor of the man who logged its maiden dive. Inside her “exotic but necessary ‘lab coat,’ ”, she was protected from the squeeze, the bends, and so many of the maladies that had plagued earlier divers, free to ponder the “twilight dwellers” she encountered. She was an explorer seeking to understand—not exploit—the oceans and their inhabitants. 

But even the bottom of the ocean can’t escape capitalism’s squeeze. Two years after her dive in the JIM suit, she and Hawkes sought funding to develop a “bubble sub”—a spherical manned submersible that would offer extended access to the deep and be a boon for oceanographic research. Despite their prominence in the diving and engineering communities, they came up empty. Instead, they started a company, Deep Ocean Technology, and pivoted to a remotely operated vehicle dedicated to oil-rig inspection, maintenance, and repair. After a pitch to Chevron failed, Shell Oil became their first customer.

The Nature of Human Nature

In Earle’s vast body of writing about the oceans and her time within them, she exhibits an uneasy sense of acceptance that marine exploration is inextricable from extractive industry.

After the JIM dive provoked a desire “to see if new ways could be developed to go deeper, stay longer, and do more once there,” she consulted executives and managers to learn how these “pioneers” had turned offshore drilling away from its “Wild West” early days to a “far more sophisticated” industry whose platforms used technology and protocols similar to those found in the space program. She marveled at the precision with which these companies got the job done—even if the job itself endangered the oceans. Despite the harm they cause, Earle maintains that we’re all “beneficiaries of the industries many love to hate—oil and gas.”

As much as anyone, though, Earle understands the source of this abhorrence. Visiting the Exxon Valdez spill in Alaska in 1989 alongside officials from the National Oceanic and Atmospheric Administration and U.S. Coast Guard, she approached with “as much scientific detachment as I could muster” but was soon overtaken by “a sense of despair about the nature of human nature.” On dives in the Persian Gulf in the early 1990s, after Saddam Hussein deliberately unleashed 500 million gallons of oil during the Gulf War, she lamented “the horrendous power of my species to destroy.”

On the day Earle touched the ocean’s bottom off the coast of Hawaii in 1979, nearly 60 million barrels of oil were pumped from wells around the world, roughly 20% of it coming from the oceans. Today, those figures have only grown. One hundred million barrels of oil are produced every day, 30% of it coming from the 12,000 offshore platforms that loom over the marine landscape like combustible floating cities. Hundreds of millions of gallons each year are released back into the oceans, poisoning the marine environments that so fascinated both Cousteau and Earle.

In the decades since the 1979 dive, Earle has remained a steadfast advocate for the oceans’ protection, serving as chief scientist at NOAA and president and chair of Mission Blue, an organization working to protect marine areas. But diving’s interwoven history of exploration and exploitation can trap even a decorated naturalist like so many fish in a net.

“Of course the economic uses of the ocean matter—extraction of oil, gas, minerals, fresh water and wildlife, transportation, tourism, real estate enhancement, and much more,” she wrote in 2009. But more importantly, the oceans matter because they “hold the world on a steady course,” she continued. “The big question is, what can we do to take care of the blue world that takes care of us?”

The answers are fraught. Polymetallic nodules, billions of tons of which are strewn across the oceans’ abyssal plains, are small black stones rich in lithium, cobalt, nickel, copper, and manganese—precisely the natural resources needed in massive quantities to create the batteries and other infrastructure that might power a transition away from fossil fuels. Extracting them from the silt and sediment on the seafloor is currently illegal in international waters, but Norway’s parliament voted earlier this year to open up more than 100,000 square miles of its national waters to commercial mining. Closer to home, House Republicans have introduced a bill that aims to promote the country’s stake in the industry.

Earle once described deep-sea mining as an “inevitable development” and more recently called it a “clear and present danger” to both marine life and the oceans’ role in carbon sequestration. The process would rely on much of the technology developed to aid the offshore drilling industry, including remotely operated vehicles.

“Ultimately,” Earle wrote, “the decisions about mining the deep sea will most likely be based on the usual short-term perception of economic values.” That bodes poorly for the thousands of creatures still being discovered in the deep sea, whose habitats are now susceptible to the whims of mining merchants.

In her writing, Earle points often to the wisdom of Swiss oceanographer and submarine designer Jacques Piccard, who once suggested that the twin challenges of diving to the deep sea and removing its most valuable resources were giving way to an altogether more exciting challenge: “the one which concerns the preservation of the sea.” If diving technology served as a tool for extraction, the knowledge it created might also help undo the harms caused by our return to the sea.

“By breaking the seal of the surface and penetrating the mirror that reflects the sky, man will reap a beautiful and incredible harvest in the decades ahead,” Piccard wrote in 1961’s Seven Miles Down. “We are prone to speak of conquering nature. If man has a weakness it is this vanity. The best we can ever hope to do is to understand nature and obey it.”