Then one week I worked for Grampa, “walking beans”—hopping the rows and hoeing or pulling weeds and volunteer corn—in return for five 2-lb. bags of Snickers; there had been a candy sale at Woolworth’s. Every morning I got up at six, did my regular chores, and rode in the back of the pickup to a section of field I had never seen. Each day I was dropped there alone in the field with a mason jar of ice-water and my great-grandmother’s hoe, which was worn by work into a kidney-shaped sliver and sharpened to a silver half moon. Around noon my mother would arrive in the pickup, bucking along the rough end rows with my lunch beside her on the dusty bench seat. The itch of dirt and soybeans. At suppertime it was back to the farm in the back of the truck, to hose the black dirt from my legs and hair before Mom would serve me real macaroni-and-cheese or tater-tots with meat.

I finished up that bean field early the next week, and came home early, in the heat of the day. We were walking up from the front gate when Mom stopped and slowly cocked her head, and turned her nose to the air. “What’s that stink? It’s been a couple days, now. Is something dead?” she raised her eyebrows. I ran around to the back yard, balked at the stench, walked toward the barrel.

The fossil record indicates five major mass extinctions, periods when more than half of all living species (not counting bacteria) on Earth have gone extinct. At the end of the Cretaceous Period, 65 million years ago, was the mass extinction that claimed the dinosaurs; the climate dramatically changed as a result of a meteor impact, or of increased volcanic activity, as the continents drifted toward their present positions. At the end of the Triassic Period, 199 to 214 million years ago, massive volcanic eruptions warmed the climate and acidified the ocean, killing most of the ocean’s species and nearly half of those on land. The Permian Period ended, 251 million years ago, with the Earth’s worst mass extinction yet for marine and land animals: 95 percent of all species extirpated by drastically changing climate. Before that was the Late Devonian Extinction, 360-375 million years ago, and the first Great Dying roughly 439 million years ago, at the end of the Ordovician Period.