Over the last half a billion years, there have been five mass extinctions, when the diversity of life on earth suddenly and dramatically contracted. Scientists around the world are currently monitoring a predicted sixth extinction, which this time around, will be caused by us. In her book, The Sixth Extinction: An Unnatural History, author Elizabeth Kolbert describes traveling the world to document the mass extinction of species that seems to be unfolding before our eyes. She recently talked with Cincinnati Zoo’s Thane Maynard about her book, and what she’s discovered.