When Elizabeth Kolbert joined The New Yorker in 1999, after more than a decade covering New York politics as a reporter and columnist for The New York Times, she began gravitating to environmental issues.

“The magazine has a history in this area,” she told me in one of two recent conversations. “They’d published Rachel Carson. It was unoccupied territory at the time.”

This week Ms. Kolbert, 52, published her second major book on the environment, “The Sixth Extinction: An Unnatural History” (Henry Holt), which asks science-based questions about whether humans might be causing mass extinction. (Her first, “Field Notes From a Catastrophe,” was about climate change.)

What follows is an edited and condensed version of our conversations.

Q. How does a journalist take on a topic this big — mass extinction?