The One-Sentence Version

Elizabeth Kolbert travels across the planet to document a sixth mass extinction already in progress, one caused not by asteroids or ice ages but by human activity unfolding faster than scientists once thought possible.

The Core Idea

In 4.5 billion years of Earth history there have been five mass extinctions. The most recent wiped out the non-avian dinosaurs. What Kolbert documents is that a sixth mass extinction is already underway, and unlike the previous five, this one has a single cause: Homo sapiens. Using on-the-ground fieldwork and scientific reporting, she travels to the Amazon, the Great Barrier Reef, an Italian cave, and a Panamanian frog sanctuary to show readers the crisis at species level.

Kolbert's central argument is not that extinction is new but that the rate is unprecedented. The background extinction rate over most of Earth's history is roughly one species per million per year. Current rates are estimated at 1,000 to 10,000 times higher. Habitats are shrinking, oceans are acidifying, and species are being relocated across continents faster than evolution can respond. The sixth extinction is distinguished from the previous five by one thing: it is happening in real time, and we are watching it.