BEFORE IT WAS an ocean of grasses, the prairie was a shallow sea. Salt water sloshed for millennia, as rounded grains of quartz sand were swept from the dry land into the surf. When the quartz finally settled—down into the beds thousands of yards thick—trilobites, those bottom-feeding arthropods, crawled onto the large shelf of sand.
Generation after generation of trilobites, a number stretching to near infinity, would die, covered by sediment, sludge, and mud. Weight and time then would transfigure the trilobites into a massive underground sea of gas- and oil-rich rock.
As the sediment settled, a large delta emerged—swamps, lagoons, meandering rivers, and vast forested floodplains. Trees—expanding twelve feet in diameter and more than one hundred feet tall—grew like a prehistoric version of the Everglades.
Plants growing in the swamps, lagoons, and marshes perished. They, too, were submerged underwater. Oxygen could not exist in the shallow bowls of plant debris, so the plants were broken down, slowly but inexorably, by anaerobic bacteria. But a thick layer of plant material did not fully decompose, and vast beds of peat accumulated.
The surrounding streams changed course and, when they did, sprinkled sand and silt atop the peat. Layer upon layer—some more than fifty feet deep—weighed down the peat beds that, over time, transformed into seams of lignite coal only a few feet thick.
Volcanoes shot ash into the atmosphere. The ash floated on the airstreams. Ancient waterways flowing north and east carried silt and clay. Tyrannosaurus rex, triceratops, and other dinosaurs roamed the ancient, verdant land.
When a meteor struck what is now Mexico, the Age of Dinosaurs abruptly ceased, a blanket of dust and sand covering these creatures’ thewy flesh. Ferns wilted and died. The weight of it all pressed the coal and oil down.
Then came the great sheets of ice—miles thick—from the north. Boulders were picked up like tennis balls and dropped along the way. The middle of what would become the North American continent was bulldozed and reshaped into a vast, open plain.