A deep-bellied rumble reverberates through an expanse of tired, wrinkled badlands. A diesel truck sits atop a mesa, a metal shaft extending downward from the rear of its bed, piercing the earth like a stinger. The shaft spins 20 times per second. Hundreds of feet below, its diamond-crusted end grinds through layer after layer of sedimentary stone. The hard-hat workers running this rig often drill for gold or other valuable metals. But today they’re drilling for something entirely different. The workers idle the drill, and the roar abates. They hoist a cylinder from the hole, as long and skinny as a person’s arm, and hurry it into a tent and onto a table. Hidden inside the muddy plastic cylinder is a section of core from a long-buried world. For stone, it is surprisingly fragile. The sheath protects it from swelling and crumbling.
Paleontologist Paul Olsen kneels for a look at the round cross-section of stone at the end of the core. It is bluish, cluttered with gray, oblong shapes.
All day and night for the past week, core sections have emerged from the drill hole every few minutes. Their blue, gray or reddish colors mirror the stone layers exposed on the surrounding badlands here in Arizona’s Petrified Forest National Park. This landscape, comprising the so-called Chinle formation, coalesced from layers of mud and gravel laid down over 200 million years ago. Back then, this area was a land of tropical forests, floodplains, lakes and meandering rivers.
Olsen and his colleagues will study these cores for years to come. But even now, Olsen, with Columbia University’s Lamont-Doherty Earth Observatory in Palisades, N.Y., can intuit something about how these ancient landscapes evolved. The reddish layers represent dry patches of ground where oxygen seeped into the soil and rusted the iron minerals in it. The blue-gray layers show where the drill penetrated the bed of an ancient lake or river; low oxygen levels prevented the iron minerals from rusting. Some cores even hold traces of ancient plant roots or animal burrows.
