Andrew Knoll is the Fisher Professor of Natural History in the Department of Earth and Planetary Sciences at Harvard University. Andy’s work straddles the line between the early evolution of life on Earth and our planet’s environmental history. He has written numerous books on these subjects, most recently A Brief History of Earth: Four Billion Years in Eight Chapters (Custom House). In this episode, Robinson and Andy discuss when and how life arose on earth—and, just as importantly, what and how we know about it. Then they turn to some related topics, such as the diversity of microbial life on Earth and how it shaped our environment. They finish off with the possibility of life on Mars, as Andy was part of NASA’s MER mission to Mars, which examined the soil and geology of Mars’s surface through two rovers, Spirit and Opportunity.A Brief History of Earth: https://a.co/d/dLrMhVzOUTLINERobinson’s Website: http://robinsonerhardt.comRobinson Erhardt researches symbolic logic and the foundations of mathematics at Stanford University. Join him in conversations with philosophers, scientists, weightlifters, artists, and everyone in-between.