There aren’t very many symbols in The Sixth Extinction. However, Kolbert has an interesting habit of ending each chapter with a symbolically loaded image. At the end of Chapter 12, Kolbert visits the Grotte des Combarelles, a prehistoric cave in France, which leads her to realize how “mad” ancient human beings must have been to explore the world. In this way, the cave symbolizes the drive and mad ambition of the human species—qualities which have led human beings to colonize the entire world.

Kolbert writes about the Great Barrier Reef, located off the coast of Australia, and how the increased acidity of the water has been destroying it for the last few decades. In this way, the Great Barrier Reef is a synecdoche (symbol where a part of something represents the whole) for the planet itself, and a symbol for the way that human behavior is destroying the planet’s beauty and complexity.