The Sixth Extinction identifies the precarious period we presently inhabit. Elizabeth Kolbert’s Pulitzer Prize–winning book of the same name inspires the title. In her masterful opus, Kolbert charts Earth’s previous five mass extinctions—from the Ordovician-Silurian events, occurring about 444 million years ago and resulting in the loss of around 85 percent of marine life, to the Cretaceous-Paleogene event some 66 million years ago, precipitated by an asteroid hitting the planet’s surface near…