I AM SITTING ON THE WOODEN DOCK that extends over the drab waters of Acton Lake. The lake itself is nothing unusual, though I often wish that it were. It is not as if, fifteen thousand years ago, the fluted, rock-bearing snout of some south-extended glacier had begun to pool and retreat in the wakening Ohio spring, leaving behind a strand of sweet water—the reflecting waters of mastodon herds and cold adapted spruce. Unlike the fingered extensions of Lake Erie and Lake Michigan, or even the kettle lakes of Champaign County to the north, Acton Lake had no such romantic origins. It was created by human hands, the work of convicts impressed not long ago into the service of the state. Nothing exceptional.

      And yet it has all the features of the ideal lake. In summer it stratifies. Layers of warm, light water drift on the cool, denser strata below. These upper waters mingle with the atmosphere. Winds from among the corn rows press the surface, sending molecules of oxygen through the tearing lake skin, riding the currents deep into the mixed layer. Streams bring an abundance of the nutrient elements, especially nitrogen and phosphorus from the neighboring farm fields and silicon from the channel rocks. Carbon, the most important element of all, comes to the lake from the air, from carbon dioxide, and from the weathering of ancient carbonates—carbonates layered long ago by shallow seas that once crept over this land, back when the Earth’s surface was arranged in unfamiliar ways. There is nourishment aplenty for the drifting phytoplankton and zooplankton and for the microscopic rotifers turning like pinwheels in the lapping shallows, and on up the food chain to the bluegill, to the rugged, omnivorous carp that wants for nothing. Acton Lake, in the parlance of limnology, is eutrophic, well-fed, teeming with life.

      In summer, beneath the warm, oxygen-rich surface, lies another lake. Limnologists call it the hypolimnion, but it is really another world. In the depths of the hypolimnion, water meets mud, not sky; the lake is chill and dark. Things sink in a summer-long procession of death and decomposing. Gradually the dissolved molecular oxygen in these lower waters gives out, followed by anything to which oxygen is attached: nitrate, nitrite, sulfate, finally even carbon dioxide. The order is always the same. In their place noxious gases evolve: ammonia, hydrogen sulfide, more than likely a trace of methane. It is as though the hypolimnion came from another planet, from another Earth-age, from an Earth fecund with the unoxidized molecules of life. To this hidden lake the settling organisms yield up their cellular nitrogen and phosphorus and carbon. The knot that photosynthesis has tied is quietly undone, unraveled in lightlessness, as respiration releases things back into the unformed, into the possible. With no oxygen, the muds begin to decompose, to release manganese and iron and more phosphorus from their locked positions in the once robust but now failing fabric of metal oxides. By August the lower lake is a chemical brew, an exotic, stygian place, lurking just below the casual swimmer’s feet. These two lakes, irreconcilable yet interdependent in the drifting, slow exchange of matter, coexist by virtue of their different densities, one curious lake perched above another.

      It is in the seasons of a lake that you can sense the miracle of water at work. As summer approaches and the surface warms, the molecules of the liquid quicken their motion. Energetic and vibrant, they spin from confining clusters and, like dancers in the quickening tempo of the dance, carve out more space for themselves, room to turn and pirouette, tiny maneuvers. A warmer parcel of water expands, occupies more space, becomes less dense, a thing of lightness. It fills the surface and isolates below it the cooler waters of the deep. Sheltered from the summer air, from the sun’s light, the lower lake lies in its chill repose. Its molecules are held more tightly, held in the thrall of hydrogen bond linked upon hydrogen bond, a vast and sprawling bridgework of more rigid design. These molecules of the lower lake are more compact, more grave and circumscribed in their motion, less given to the wild kinetic flights that higher temperatures occasion in matter. Epilimnion and hypolimnion, so utterly different. And yet, like a volume of Rutherford and a volume of Yeats casually stacked upon a cluttered desk, they are written in a common, endlessly variable language. The atom’s emptiness; the wild profusion of Innisfree.

      As autumn approaches, there comes a subtle tug toward unity, toward the mingling of waters and the merging of worlds. In the crisp air of late September and early October, and particularly at night, as the stars rise and fall above cloudless skies, the warm surface lake radiates heat away into the autumn air. Its temperature becomes more nearly that of the deep waters. If you run the cable of a temperature probe through the water column from top to bottom, the thin needle barely moves: constant temperature, constant density, all the way down.

      In this fine state of balance, a gentle night wind, sloughing the clattering leaves of the maples, is enough to set the poised waters streaming. Masses of stagnant hypolimnion plume upward, mushroom and bend, curl like ancient scrolls through the upper lake. In exchange, the surface waters plunge downward and spread along the fetid sulfidic muds, bringing with them a veritable hailstorm of that fateful and aggressive molecule, oxygen. At fall overturn, the hypolimnion becomes stripped of its methane and sulfides. Encountering oxygen, iron and manganese are oxidized and rain as solids from the lake again, as they must have in ancient seas. The upwelled phosphorus and nitrogen, not to be lost in the economy, spark a fall bloom of algae, a momentary green suffusion on the surface lake. Things enter from below, long stored away; the lake’s past comes to light.

      Winter stratification in late October seems anticlimax. Beneath the thin veneer of ice that spreads across the surface, the lake is more homogeneous. Today a gray lake stretches flat under gray sky, a dormant sheet, as expressionless as shale. The brilliant canopy of trees has become an outreaching of spidery black limbs, and the drama of overturn has long passed. You can see ice beginning to build out from the docks, in the tentative, molecule-by-molecule way that ice builds, freezing, as ice does, from the surface down.

      When I return the lake will be frozen and perfectly still. Like Bonney and Fryxell. Like Vanda. For now, I start the car, turn it south toward home, and leave Acton Lake in its dormancy, hoping that in a few months I will see it again.

      When I tell people there are lakes in Antarctica, they think surely I am joking. “Lakes there?” they ask. “How can that be? It’s all ice and snow. Penguins running around.” Then, when I assure them that it’s true, they ask, in a more assertive tone, “But they’re frozen, of course?” And I say, “Well, yes, there’s ice on the surface, but below there’s liquid water, sometimes as deep as two hundred feet.” Then they ask—and this is inevitable—“Are there fish?” I say, “No, not a single one.” “Hmmm,” they respond, incredulous, “a lake without fish. Does anything live in them, at all?” And they emphasize “at all.” “Only algae and bacteria,” I say. “Nothing you can actually see with your eyes. Except for the mats of algae, which are tiny columns and pinnacles on the bottom, far below the ice.”

      But then it is precisely what is not there, what has never been there, that makes the lakes—indeed, the whole continent on which they lie—so strange and so important.

      For me these absences, and the simplicity to which they give rise, were the key. The lakes are the most isolated inland waters in the world. Landlocked, they are without spillage or outflow; each has only a few streams, and these hold water for only a few weeks out of the year. They are ice-covered, so that very little in the form of dust or snow enters them from the air. And, of course, there is never rain. That in itself makes them magic. How can you have a lake without rain? A lake without fish, maybe, but a lake without rain? A land without rain. A whole continent. Such living things as there are are mostly microscopic—algae, bacteria, yeast, a minimalist’s tableau. And into this setting, stark and largely inorganic, Martian almost, the elements come—nitrogen, phosphorus, the metals—unheralded, but replete with possibilities, with lives to be lived.

      It would be no exaggeration to say that I was obsessed with the lakes, and especially with the metals that coursed through them like bits and pieces of an invisible wind. In this seemingly fantastical concern,