The mass extinction that killed off the dinosaurs was known to have coincided with Earth getting hit by an asteroid. Next time, we may be the asteroid, according to Elizabeth Kolbert's new book "The Sixth Extinction: An Unnatural History." Kolbert writes that humans are not only "witnessing one of the rarest events in life's history, we are also causing it."
From the Archives: Elizabeth Kolbert on Earth's Sixth Mass Extinction
Elizabeth Kolbert, staff writer for New Yorker Magazine; and author of "The Sixth Extinction: An Unnatural History" and "Field Notes from a Catastrophe: Man, Nature, and Climate Change"