Because the turtles [I was studying in Costa Rica] come out to nest after dark, much of my work was done at night. There was a great deal of waiting between turtles, plenty of time to sit on a driftwood log and think. In the first years of my research I was often the only one on the beach for miles. After ten or twenty minutes of sitting without using my flashlight, my eyes adapted to the dark and I could make out forms against the brown-black sand: the beach plum and coconut palm silhouettes in back, the flicker of the surf in front, sometimes even the shadowy outline of a trailing railroad vine or the scurry of a ghost crab at my feet. The air was heavy and damp with a distinctive primal smell that I can remember but not describe. The rhythmic roar of the surf a few feet away never ceased -- my favourite sound. I hear it as I write in my landlocked office in New Jersey. And then, with ponderous, dramatic slowness, a giant turtle would emerge from the sea.

Usually I would see the track first, a vivid black line standing out against the lesser blackness, like the swath of a bulldozer. If I was closer, I could hear the animal's deep hiss of breath and the sounds of her undershell scraping over logs. If there was a moon, I might see the light glistening off the parabolic curve of the still wet shell. Size at night is hard to determine: even the sprightly 180-pounders, probably nesting for the first time, looked big when nearby, but the 400-pound ancients, with shells nearly four feet long, were colossal in the darkness. Then when the excavations of the body pit and egg cavity were done, if I slowly parted the hind flippers of the now-oblivious turtle, I could watch the perfect white spheres falling and falling into the flask-shaped pit scooped into the soft sand.

Falling as they have fallen for a hundred million years, with the same slow cadence, always shielded from the rain or stars by the same massive bulk with the beaked head and the same large, myopic eyes rimmed with crusts of sand washed out by tears. Minutes and hours, days and months dissolve into eons. I am on an Oligocene beach, an Eocene beach, a Cretaceous beach -- the scene is the same. It is night. The turtles are coming back, always back; I hear a deep hiss of breath and catch a glint of wet shell as the continents slide and crash, the oceans form and grow. The turtles were coming here before here was here. At Tortuguero I learned the meaning of place, and began to understand how it is bound up with time.