Astrobiologist Caleb Scharf joins Michael Shermer for a wide-ranging conversation about the past, present, and future of our relationship with space. Drawing on his new book The Giant Leap, Scharf explains why human expansion beyond Earth may be less a choice than an evolutionary development, and he walks through the physics, history, and personalities that shaped our journey off the planet.

Scharf also explains the biological toll of radiation and microgravity, and why terraforming Mars is probably unrealistic and why our future might rely more on building vast rotating habitats in space than on settling other planets.

Caleb Scharf is an astrobiologist and recipient of the 2022 Carl Sagan Medal. He was Director of Astrobiology at Columbia University in New York and is now the Senior Scientist for Astrobiology at the NASA Ames Research Center in Silicon Valley. He is author of more than 120 scientific papers and over 500 popular science articles. His new book is The Giant Leap: Why Space is the Next Frontier in the Evolution of Life.