In the Prologue, author Elizabeth Kolbert addresses theories of the beginning of human existence. She considers the emergence of this new species roughly two hundred thousand years ago, a species with no name but with “the capacity to name things” (1). The resourceful members of this species manage to overcome their genetic flaws, notably their lack of speed and slow rate of procreation. Despite these obstacles, the species manages to cross land and sea, to spread throughout the world, and to exist in very diverse environments.

The astounding success of this species, Homo sapiens, leads to an unprecedented population boom which in turn results in humans purposefully and ignorantly changing the biosphere to suit their species’ ever-increasing needs. Over time, human beings accomplish what no other species ever has: permanently altering the atmosphere and life on the planet.

Kolbert discusses the Big Five, previous catastrophic instances of radical change that have impacted Earth. The history of these five events is being discovered right at the time that humans are facing what they have, over time, created: a possible Sixth Extinction. The author describes the Sixth Extinction in thirteen chapters that focus on a species—Homo sapiens—that is representative of its time; however, Kolbert also argues that this species’ actions herald a future mass extinction in modern times, including some signs that are already underway.