When underwater researchers realized that the Navy had no intention of pursuing a promised exploration program, there was a pained outcry. Partly to placate its critics, the Navy provided funding for a more advanced submersible, to be operated by the Woods Hole Oceanographic Institution of Massachusetts. CalledAlvin, in somewhat contracted honor of the oceanographer Allyn C. Vine, it would be a fully maneuverable minisubmarine, though it wouldn’t go anywhere near as deep as theTrieste. There was just one problem: the designers couldn’t find anyone willing to build it. According to William J. Broad inThe Universe Below : “No big company like General Dynamics, which made submarines for the Navy, wanted to take on a project disparaged by both the Bureau of Ships and Admiral Rickover, the gods of naval patronage.” Eventually, not to say improbably,Alvin was constructed by General Mills, the food company, at a factory where it made the machines to produce breakfast cereals.

As for what else was down there, people really had very little idea. Well into the 1950s, the best maps available to oceanographers were overwhelmingly based on a little detail from scattered surveys going back to 1929 grafted onto, essentially an ocean of guesswork. The Navy had excellent charts with which to guide submarines through canyons and around guyots, but it didn’t wish such information to fall into Soviet hands, so it kept its knowledge classified. Academics therefore had to make do with sketchy and antiquated surveys or rely on hopeful surmise. Even today our knowledge of the ocean floors remains remarkably low resolution. If you look at the Moon with a standard backyard telescope you will see substantial craters—Fracastorious, Blancanus, Zach, Planck, and many others familiar to any lunar scientist—that would be unknown if they were on our own ocean floors. We have better maps of Mars than we do of our own seabeds.

At the surface level, investigative techniques have also been a trifle ad hoc. In 1994, thirty-four thousand ice hockey gloves were swept overboard from a Korean cargo ship during a storm in the Pacific. The gloves washed up all over, from Vancouver to Vietnam, helping oceanographers to trace currents more accurately than they ever had before.

TodayAlvin is nearly forty years old, but it still remains America’s premier research vessel. There are still no submersibles that can go anywhere near the depth of the Mariana Trench and only five, includingAlvin, that can reach the depths of the “abyssal plain”—the deep ocean floor—that covers more than half the planet’s surface. A typical submersible costs about $25,000 a day to operate, so they are hardly dropped into the water on a whim, still less put to sea in the hope that they will randomly stumble on something of interest. It’s rather as if our firsthand experience of the surface world were based on the work of five guys exploring on garden tractors after dark. According to Robert Kunzig, humans may have scrutinized “perhaps a millionth or a billionth of the sea’s darkness. Maybe less. Maybe much less.”

But oceanographers are nothing if not industrious, and they have made several important discoveries with their limited resources—including, in 1977, one of the most important and startling biological discoveries of the twentieth century. In that yearAlvin found teeming colonies of large organisms living on and around deep-sea vents off the Galápagos Islands—tube worms over ten feet long, clams a foot wide, shrimps and mussels in profusion, wriggling spaghetti worms. They all owed their existence to vast colonies of bacteria that were derivingtheir energy and sustenance from hydrogen sulfides—compounds profoundly toxic to surface creatures—that were pouring steadily from the vents. It was a world independent of sunlight, oxygen, or anything else normally associated with life. This was a living system based not on photosynthesis but on chemosynthesis, an arrangement that biologists would have dismissed as preposterous had anyone been imaginative enough to suggest it.

Huge amounts of heat and energy flow from these vents. Two dozen of them together will produce as much energy as a large power station, and the range of temperatures around them is enormous. The temperature at the point of outflow can be as much as 760 degrees Fahrenheit, while a few feet away the water may be only two or three degrees above freezing. A type of worm called an alvinellid was found living right on the margins, with the water temperature 140 degrees warmer at its head than at its tail. Before this it had been thought that no complex organisms could survive in water warmer than about 130 degrees, and here was one that was surviving warmer temperatures than thatand extreme cold to boot. The discovery transformed our understanding of the requirements for life.

It also answered one of the great puzzles of oceanography—something that many of us didn’t realize was a puzzle—namely, why the oceans don’t grow saltier with time. At the risk of stating the obvious, there is a lot of salt in the sea—enough to bury every bit of land on the planet to a depth of about five hundred feet. Millions of gallons of fresh water evaporate from the ocean daily, leaving all their salts behind, so logically the seas ought to grow more salty with the passing years, but they don’t. Something takes an amount of salt out of the water equivalent to the amount being put in. For the longest time, no one could figure out what could be responsible for this.

Alvin’s discovery of the deep-sea vents provided the answer. Geophysicists realized that the vents were acting much like the filters in a fish tank. As water is taken down into the crust, salts are stripped from it, and eventually clean water is blown out again through the chimney stacks. The process is not swift—it can take up to ten million years to clean an ocean—but it is marvelously efficient as long as you are not in a hurry.

Perhaps nothing speaks more clearly of our psychological remoteness from the ocean depths than that the main expressed goal for oceanographers during International Geophysical Year of 1957–58 was to study “the use of ocean depths for the dumping of radioactive wastes.” This wasn’t a secret assignment, you understand, but a proud public boast. In fact, though it wasn’t much publicized, by 1957–58 the dumping of radioactive wastes had already been going on, with a certain appalling vigor, for over a decade. Since 1946, the United States had been ferrying fifty-five-gallon drums of radioactive gunk out to the Farallon Islands, some thirty miles off the California coast near San Francisco, where it simply threw them overboard.

It was all quite extraordinarily sloppy. Most of the drums were exactly the sort you see rusting behind gas stations or standing outside factories, with no protective linings of any type. When they failed to sink, which was usually, Navy gunners riddled them with bullets to let water in (and, of course, plutonium, uranium, and strontium out). Before it was halted in the 1990s, the United States had dumped many hundreds of thousands of drums into about fifty ocean sites—almost fifty thousand of them in the Farallons alone. But the U.S. was by no means alone. Among the other enthusiastic dumpers were Russia, China, Japan, New Zealand, and nearly all the nations of Europe.

And what effect might all this have had on life beneath the seas? Well, little, we hope, but we actually have no idea. We are astoundingly, sumptuously, radiantly ignorant of life beneath the seas. Even the most substantial ocean creatures are often remarkably little known to us—including the most mighty of them all, the great blue whale, a creature of such leviathan proportions that (to quote David Attenborough) its “tongue weighs as much as an elephant, its heart is the size of a car and some of its blood vessels are so wide that you could swim down them.” It is the most gargantuan beast that Earth has yet produced, bigger even than the most cumbrous dinosaurs. Yet the lives of blue whales are largely a mystery to us. Much of the time we have no idea where they are—where they go to breed, for instance, or what routes they follow to get there. What little we know of them comes almost entirely from eavesdropping on their songs, but even these are a mystery. Blue whales will sometimes break off a song, then pick it up again at the same spot six months later. Sometimes they strike up with a new song, which no member can have heard before but which each already knows. How they do this is not remotely understood. And these are animals that must routinely come to the surface to breathe.

For animals that need never surface, obscurity can be even more tantalizing. Consider the fabled giant squid. Though nothing on the scale of the blue whale, it is a decidedly substantial animal, with eyes the size of soccer balls and trailing tentacles that can reach lengths of sixty feet. It weighs nearly a ton and is Earth’s largest invertebrate. If you dumped one in a normal household swimming pool, there wouldn’t be much room for anything else. Yet no scientist—no person as far as we know—has ever seen a giant squid alive. Zoologists have devoted careers to trying to capture, or just glimpse, living giant squid and have always failed. They are known mostly from being washed up on beaches—particularly, for unknown reasons, the beaches of the South Island of New Zealand. They must exist in large numbers because they form a central part of the sperm whale’s diet, and sperm whales take a lot of feeding.34

According to one estimate, there could be as many as thirty million species of animals living in the sea, most still undiscovered. The first hint of how abundant life is in the deep seas didn’t come until as recently as the 1960s with the invention of the epibenthic sled, a dredging device that captures organisms not just on and near the seafloor but also buried in the sediments beneath. In a single one-hour trawl along the continental shelf, at a depth of just under a mile, Woods Hole oceanographers Howard Sandler and Robert Hessler netted over 25,000 creatures—worms, starfish, sea cucumbers, and the like—representing 365 species. Even at a depth of three miles, they found some 3,700 creatures representing almost 200 species of organism. But the dredge could only capture things that were too slow or stupid to get out of the way. In the late 1960s a marine biologist named John Isaacs got the idea to lower a camera with bait attached to it, and found still more, in particular dense swarms of writhing hagfish, a primitive eel-like creature, as well as darting shoals of grenadier fish. Where a good food source is suddenly available—for instance, when a whale dies and sinks to the bottom—as many as 390 species of marine creature have been found dining off it. Interestingly, many of these creatures were found to have come from vents up to a thousand miles distant. These included such types as mussels and clams, which are hardly known as great travelers. It is now thought that the larvae of certain organisms may drift through the water until, by some unknown chemical means, they detect that they have arrived at a food opportunity and fall onto it.

So why, if the seas are so vast, do we so easily overtax them? Well, to begin with, the world’s seas are not uniformly bounteous. Altogether less than a tenth of the ocean is considered naturally productive. Most aquatic species like to be in shallow waters where there is warmth and light and an abundance of organic matter to prime the food chain. Coral reefs, for instance, constitute well under 1 percent of the ocean’s space but are home to about 25 percent of its fish.

Elsewhere, the oceans aren’t nearly so rich. Take Australia. With over 20,000 miles of coastline and almost nine million square miles of territorial waters, it has more sea lapping its shores than any other country, yet, as Tim Flannery notes, it doesn’t even make it into the top fifty among fishing nations. Indeed, Australia is a large net importer of seafood. This is because much of Australia’s waters are, like much of Australia itself, essentially desert. (A notable exception is the Great Barrier Reef off Queensland, which is sumptuously fecund.) Because the soil is poor, it produces little in the way of nutrient-rich runoff.

Even where life thrives, it is often extremely sensitive to disturbance. In the 1970s, fishermen from Australia and, to a lesser extent, New Zealand discovered shoals of a little-known fish living at a depth of about half a mile on their continental shelves. They were known as orange roughy, they were delicious, and they existed in huge numbers. In no time at all, fishing fleets were hauling in forty thousand metric tons of roughy a year. Then marine biologists made some alarming discoveries. Roughy are extremely long lived and slow maturing. Some may be 150 years old; any roughy you have eaten may well have been born when Victoria was Queen. Roughy have adopted this exceedingly unhurried lifestyle because the waters they live in are so resource-poor. In such waters, some fish spawn just once in a lifetime. Clearly these are populations that cannot stand a great deal of disturbance. Unfortunately, by the time this was realized the stocks had been severely depleted. Even with careful management it will be decades before the populations recover, if they ever do.

Elsewhere, however, the misuse of the oceans has been more wanton than inadvertent. Many fishermen “fin” sharks—that is, slice their fins off, then dump them back into the water to die. In 1998, shark fins sold in the Far East for over $250 a pound. A bowl of shark fin soup retailed in Tokyo for $100. The World Wildlife Fund estimated in 1994 that the number of sharks killed each year was between 40 million and 70 million.

As of 1995, some 37,000 industrial-sized fishing ships, plus about a million smaller boats, were between them taking twice as many fish from the sea as they had just twenty-five years earlier. Trawlers are sometimes now as big as cruise ships and haul behind them nets big enough to hold a dozen jumbo jets. Some even use spotter planes to locate shoals of fish from the air.

It is estimated that about a quarter of every fishing net hauled up contains “by-catch”—fish that can’t be landed because they are too small or of the wrong type or caught in the wrong season. As one observer told theEconomist : “We’re still in the Dark Ages. We just drop a net down and see what comes up.” Perhaps as much as twenty-two million metric tons of such unwanted fish are dumped back in the sea each year, mostly in the form of corpses. For every pound of shrimp harvested, about four pounds of fish and other marine creatures are destroyed.

Large areas of the North Sea floor are dragged clean by beam trawlers as many as seven times a year, a degree of disturbance that no ecosystem can withstand. At least two-thirds of species in the North Sea, by many estimates, are being overfished. Across the Atlantic things are no better. Halibut once abounded in such numbers off New England that individual boats could land twenty thousand pounds of it in a day. Now halibut is all but extinct off the northeast coast of North America.

Nothing, however, compares with the fate of cod. In the late fifteenth century, the explorer John Cabot found cod in incredible numbers on the eastern banks of North America—shallow areas of water popular with bottom-feeding fish like cod. Some of these banks were vast. Georges Banks off Massachusetts is bigger than the state it abuts. The Grand Banks off Newfoundland is bigger still and for centuries was always dense with cod. They were thought to be inexhaustible. Of course they were anything but.

By 1960, the number of spawning cod in the north Atlantic had fallen to an estimated 1.6 million metric tons. By 1990 this had sunk to 22,000 metric tons. In commercial terms, the cod were extinct. “Fishermen,” wrote Mark Kurlansky in his fascinating history,Cod , “had caught them all.” The cod may have lost the western Atlantic forever. In 1992, cod fishing was stopped altogether on the Grand Banks, but as of last autumn, according to a report inNature , stocks had not staged a comeback. Kurlansky notes that the fish of fish fillets and fish sticks was originally cod, but then was replaced by haddock, then by redfish, and lately by Pacific pollock. These days, he notes drily, “fish” is “whatever is left.”

Much the same can be said of many other seafoods. In the New England fisheries off Rhode Island, it was once routine to haul in lobsters weighing twenty pounds. Sometimes they reached thirty pounds. Left unmolested, lobsters can live for decades—as much as seventy years, it is thought—and they never stop growing. Nowadays few lobsters weigh more than two pounds on capture. “Biologists,” according to theNew York Times , “estimate that 90 percent of lobsters are caught within a year after they reach the legal minimum size at about age six.” Despite declining catches, New England fishermen continue to receive state and federal tax incentives that encourage them—in some cases all but compel them—to acquire bigger boats and to harvest the seas more intensively. Today fishermen of Massachusetts are reduced to fishing the hideous hagfish, for which there is a slight market in the Far East, but even their numbers are now falling.

We are remarkably ignorant of the dynamics that rule life in the sea. While marine life is poorer than it ought to be in areas that have been overfished, in some naturally impoverished waters there is far more life than there ought to be. The southern oceans around Antarctica produce only about 3 percent of the world’s phytoplankton—far too little, it would seem, to support a complex ecosystem, and yet it does. Crab-eater seals are not a species of animal that most of us have heard of, but they may actually be the second most numerous large species of animal on Earth, after humans. As many as fifteen million of them may live on the pack ice around Antarctica. There are also perhaps two million Weddel seals, at least half a million emperor penguins, and maybe as many as four million Adélie penguins. The food chain is thus hopelessly top heavy, but somehow it works. Remarkably no one knows how.

All this is a very roundabout way of making the point that we know very little about Earth’s biggest system. But then, as we shall see in the pages remaining to us, once you start talking about life, there is a great deal we don’t know, not least how it got going in the first place.