TWO HUNDRED FIFTY MILLION YEARS AGO THE world contained a single huge continent that scientists call Pangaea. Geological forces broke up this vast expanse. Eurasia and the Americas split apart, slicing the world into different ecological domains. Over time the two divided halves of Pangaea developed wildly different sets of plants and animals. The voyage of Christopher Columbus began to knit the pieces of Pangaea together again. The Columbian Exchange began with that voyage. To biologists, it is the most important event in the history of life on earth since the death of the dinosaurs.

The reconnecting of the world was a vast ecological upheaval with big effects on humankind. The Columbian Exchange underlies much of history like an invisible wave, sweeping along kings and queens, peasants and priests. This wave of ecological and economic change triggered by Columbus’s voyage was one of the establishing events of the modern world.