The Underworld: Journeys to the Depths of the Ocean

by Susan Casey

The earth possesses one ocean, though it’s traditionally recognized as having five major regions: the Pacific, Atlantic, Indian, Arctic, and Southern Oceans. Whenever possible, I refer to the ocean as a single entity.

The science of measuring the seabed terrain is known as bathymetry—the submarine version of topography. Bathymetric maps chart the depths and contours of the seafloor in three-dimensional relief, revealing its mountains, valleys, canyons, plains, rifts, trenches, and other undersea features.

It’s out of sight, but once it allows you a peek at its majesty, it’s never out of mind.

Even now, when every last crater on the moon has been named and interactive three-dimensional maps of Mars can be viewed on an iPhone, 80 percent of the seafloor has never been charted in any kind of sharp detail. Yet the deep ocean—defined as the waters below six hundred feet—covers 65 percent of the earth’s surface and occupies 95 percent of its living space.

In the deep, there are creatures that breathe iron and creatures with glass skeletons and creatures that communicate through their skin. Some of its creatures can turn themselves inside out. They might have two mouths or three hearts or eight legs. Or their bodies might consist of a thousand little bodies, a coordinated army. At least one deep-sea creature squirts yellow light. Some have see-through heads. Even the most ethereal among them can handle pressures that would crush a Mack truck.

place in the overall scheme of life—even our definition of life. Now it’s apparent that nature runs as a massively interconnected system, with the deep sea as its motherboard.

Other investigators, looking at seafloor mud under a microscope, noticed a filmy goo that appeared to be moving. It was everywhere, creeping through every sample, and nobody had ever seen anything like it. They named it Bathybius and wondered if it was a protoplasm that served as the foundation of life—the original primordial ooze.

One day, as the dredge was being recovered, Thomson spotted a scarlet sea urchin jammed against its side. He feared that its shell would be crushed, but the urchin remained intact. When he examined it, he was startled to see that it was panting like a dog. He stared at its rows of tube feet, its sharp blue teeth, its array of tiny spines, its round body heaving in and out. “I had to summon up some resolution before taking the weird little monster in my hand,” he admitted.

The hadal zone occupies less than 2 percent of the seafloor, but it accounts for 45 percent of the ocean’s full depth.

On the brink of utter darkness, the final traces of light appeared eerily radiant. “We were the first living men to look out at the strange illumination: And it was stranger than any imagination could have conceived,” Beebe would later write. “It was of an indefinable translucent blue quite unlike anything I have ever seen in the upper world, and it excited our optic nerves in a most confusing manner.” The blue was so piercingly vivid, he felt, that language couldn’t describe it. It was more like an emotion than a color, one that “seemed to pass materially through the eye and into our very beings.”

to study them and marvel at their weirdness. Like hot springs on land, hydrothermal vents pop up in volcanically active areas, roiling out a mix of seawater, minerals, gases, and microbes from the earth’s superheated plumbing.

What they didn’t account for, at first, was subduction. It’s an elegant system, with new crust arriving and old crust departing in perfect equilibrium, as the planet recycles itself.

The deep is a mosh pit of complexity. It is always in flux, on all scales, at all depths, in all manner of conditions.

Rose-pink anemones, electric-yellow sea stars, and lilac-purple octopuses had staked out the junction boxes like a luxury subdivision.

Here was the abyss, going about its business in synchrony with everything above it, but on its own epochal clock. I felt delight, recognition, an enveloping sense of peace. I felt my body and mind unclenching, as if hanging out on the seafloor were as relaxing as a massage.

Photosynthesis—the conversion of sunlight to energy that was thought to provide life’s only fuel—had no role here. Instead, these creatures relied on chemosynthesis: energy coming from the earth’s interior, produced by chemical reactions between fluids and rocks. The microbes were eating hydrogen sulfide—a poison to creatures on land—and oxidizing it into food for the vent animals, many of which hosted the microbes inside their bodies in a symbiotic relationship. It was a Star Wars bar-scene ecosystem that flouted all of our rules, born of an audacious chemistry experiment that has been under way for as long as the earth has had an ocean.

To Delaney’s mind, if we hope to survive whipsawing weather extremes, ecosystem upheavals, and storms of biblical intensity, we’d be wise to turn our attention downward, even if it delays our space tourism plans.

Let everything happen to you: beauty and terror. Just keep going. —Rainer Maria Rilke

After a light breakfast of biscotti, Coke Zero, and Dramamine, I pinballed down hallways and braced myself as I climbed up ladderlike stairwells and made my way across the deck to the hangar, where Lahey and his team were running the sub through its pre-dive safety check.

Lahey couldn’t have been under more pressure if he’d climbed into the chamber in Russia.

“Any experience is made richer when you share it with somebody else,” I heard Lahey say one time—explaining why every Triton sub has at least two seats—and I nodded absently, but in my mind I was thinking, No. Some of us aren’t built that way: most writers and artists, for instance, and plenty of extreme athletes. Spiritual seekers, committed readers, introverts of all stripes. Yes, having company might be pleasant or fun, but for a certain type of person that comfort is less interesting than the wilds of the psyche’s inner space—a place that doesn’t admit you with a plus-one.

“The surface of things is not where attention should rest,” the psychedelic sage Terence McKenna had counseled, and that is certainly true of the ocean.

At another wreck site, where a merchant ship sank around 1025 CE, the scuba-diving archaeologists pried three tons of multicolored glass shards from the seabed with dental picks and tweezers (dodging a territorial octopus that liked to snatch the pieces from their hands), then spent two decades reconstructing them into the world’s largest collection of medieval Islamic glass artifacts. See? Patience.

No one knows exactly how many fish live in the twilight zone—researchers keep revising their estimates upward—but we do know that it contains more fish biomass than all the other regions of the ocean combined.

I couldn’t wait to dive, and yet I also wanted to stay in the liminal space of being about to dive, with that exhilarating rush still ahead of me.

To meet the deep is to have your beliefs recalibrated, your perspective permanently tweaked.

“We’re at a point in time where we have a choice,” she said. “Here’s the thing: We didn’t know before. Fifty years ago, there was so much we didn’t know. We are now better prepared, armed with the superpower of knowledge. I tell kids, ‘Be glad that you’re a twenty-first-century human. Imagine if you didn’t have the facts about what the problems are. Imagine if you didn’t have the solutions. But you have both.’ ”

I was immersed in awe, and experiencing awe is like mainlining the truth. Above the surface, life can feel like it’s spinning apart, fracturing into pixels, dispersing like dust by the day. But here was solidity and eternity, and a reality bigger than anything we could imagine.