For thousands of years, humans have wondered whether we’re alone in the cosmos. Now, for the first time, we have the technology to investigate. The question should have an obvious answer: yes or no. But once you try to find life elsewhere, you realize it is not so simple. How do you find it over cosmic distances? What actually is life? As founding director of Cornell University’s Carl Sagan Institute, astrophysicist Lisa Kaltenegger built a team of tenacious scientists from many disciplines to create a uniquely specialized toolkit to find life on faraway worlds. In ‘Alien Earths’, she demonstrates how we can use our homeworld as a Rosetta Stone, creatively analyzing Earth’s history and its astonishing biosphere to inform this search.