Preface HOW TO LIVE IN DEEP TIME In my backyard, I have a makeshift pond: a galvanized steel tub, about two feet in diameter, outfitted with an electric filter, heating coil, algae-skimmed driftwood, and a paving stone propped up on two overturned clay flowerpots. It is a summer day, and from where I sit, reading in the shade, I hear the filter bubble softly as the sun crests the roof of the house. Soon, I hear a flipper-y noise--a muffled knock and splash of water against the tub''s sides. I put down my book. Sweeney, our three-year-old red-eared slider turtle, hoists himself--neck straining, claws scraping--up out of the water and onto the sun-soaked paving stone for his afternoon bask. Perched motionless, head tilted toward the sun''s warming rays, Sweeney appears either magnificent or absurd, depending on my mood. His neck is swamp- green, thick as a celery stick and soft as a lamb''s ear. His domed shell is as rough and ridged as damp tree bark.

When I approach him--slowly, slowly, lest he star- tle--he fixes me with eyes like two tiny wells of liquid onyx rimmed in blazing lime-green. He blinks. I hold out a blueberry, and he cracks open his beak to reveal a triangle of tongue, the softest bubblegum-pink. Many traditional cultures have myths about how the turtle got his shell. In Aesop''s fable, the tur- tle, loath to leave the comfort of her home, declines an invitation to Zeus''s wedding celebration. For this breach of etiquette, Zeus condemns her to wander the world lugging her home on her back in perpetuity. Other versions of the myth are less punishing. For the Anishinaabe, the turtle receives a beautifully painted stone shell in return for showing the god Nanabosho the best fishing spots in the river.

But evolutionary biology''s origin story is no less fantastic. The turtle''s precise phylogenetic origins are up for debate, but at some point during the Triassic, as long as 260 million years ago, what one biologist hypothesizes was a "stout lizard" began to convert the bones of its sternum into a protective body plate. Such an armored underbelly granted the creature an evolutionary edge; over time, the proto-turtle''s ribs, too, flattened and fused, turned spatulate, knit together into an elegantly curved carapace. Sweeney and his ilk are what biologists call a "highly conserved" species, an evolutionary success story. Indeed, Sweeney survived multiple mass extinction events, including the asteroid hit that wiped out the dinosaurs, scrambling back up onto his triumphal rock as his reptilian cousins perished all around him. As far as pets go, Sweeney is both more work (maintaining his outdoor aquatic environment is exhausting) and less rewarding (no cuddles) than your average mammalian pet, a dog and or cat. Yet to keep company with a turtle, archaic reminder of life''s murkier, rockier, hard-scrabble origins, has been instructive. In her poem "Landcrab I," Margaret Atwood addresses a hermit crab on a beach as secret sharer of her being.

The scowling creature, Atwood muses, has "nothing but contempt" for mammals, "with their lobes and tubers/scruples and warm milk." And yet in this "stunted child," born of "dragons [.] teeth," she nonetheless recognizes "a piece of what we are." As befits the quaint domesticity of the Victorian era, Charles Darwin imagined the origins of life on earth as a cozy affair, all lobes and warm milk. In an 1871 letter to Joseph Hooker, Darwin conjured a scene of antediluvian innocence, "some warm little pond" where, out of a rich stew of "ammonia and phosphoric salts, light, heat, electricity," a protein chain quivered and quickened. Yet over the past few decades, research on deep-sea thermal vents has led scientists to speculate that it was not in the rustic country tarn of Darwin''s imagination, but rather in the Archaean depths of a lightless ocean trench, on the mineral lip of hydrothermal vent, that life first took shape more than 3.8 billion years ago: more dragon''s tooth than amniotic sac. The solid surfaces of oceanic mineral and rock provided a base onto which a proto mem- brane could perch long enough to self-organize into a fragile bubble that would stake its claim against the surrounding chaos, islet of organization in the flux of the new earth.

The image of this original bubble, solitary pocket of inwardness winking in the deep, transfixes me, and is my preferred creation myth. It reminds me that any single biological life form is defined not by the elements that make it up, but by how the arrangement of those elements inside of a membrane differs from their arrangement outside of it and how successful that life form is at maintaining this difference across time. I am a bundle of hydrogen and oxygen and car- bon and nitrogen and calcium and phosphorous atoms that differs from the surrounding sea of those same primary elements only by dint of organization and complexity, not substance; and, in fact, over the course of my life I will swap out every atom of my original molecular makeup for atoms pulled in from outside myself, building myself from scratch like Theseus''s ship. A living organism is not so much a substance as a concentration gradient; not so much a thing as a proportional relationship maintained through the doggedness of habit. Living organisms are hardwired to spend every ounce of energy they have maintaining this gradient. The instant the organizational difference separating my little bubble of molecules from the surrounding sea of molecules collapses, I cease to exist: my elements wash, once again, back into the cosmic elemental broth that is (on the largest scale) the universe expanding toward thermodynamic equilibrium. My own little parcel of organized stuff, digging in like a barnacle on a sea rock--down-river descendent of the original bubble trembling on a vent-seam in the mineral ocean bed--succumbs to the salt tide of disorganization. The mystery of the self, then, is that every atom of our being is on loan from the universe, at every instant, from time immemorial.

This is a fact of which very few of us are ever cognizant in any consistent way. Humans don''t much like to acknowledge this loan, most likely because our brains work at time scales supremely unsuited to appreciate the nearly four-billion-year-long game of biological life on earth. We are a prideful species, hesitant to claim kinship with the primeval bubbling ooze that started the whole ball rolling. All these thoughts are swirling round in my head when suddenly, out of the literal blue, a giant jay comes screeching and thrashing through the pepper tree to peck on seeds at the feeder. Sweeney scuttles back into the water with a soft splash. He returns to the algal murk: drifting soundlessly, poking his nose among driftwood, reprising his mysterious underwater existence. Jay, turtle, tree, me: we are all cut from the same cloth. I return to my book.

To live with one eye fixed on geochemical and biological "deep time" is to practice radical humility, in the most literal sense of the world: humilitas, from humus, the Latin word for "earth." To be low to the ground, on a par with the earth''s crust, subject to the same cyclical processes of roiling, cooling, ribboning, crumbling, rise and fall and rise again. Geologists be- come so habituated to this way of counting time that they end up as philosophers. In an interview with John McPhee, geologist David Brower gave a sense of how the study of rocks had shaped his life. "You begin tuning your mind to a time scale that is the planet''s time scale," he observed. "For me, it is almost unconscious now and is a kind companionship with the earth." These essays are my attempt to follow the seams of deep time as, here and there, they have surfaced along the path of my life. They are my attempt to listen for something beyond the narrow pulse and tick of hu- man clocks, to keep companionship with the earth.