Are the inhabitants of Earth the only life forms in the universe, or could life exist elsewhere? As astronomers rapidly identify exoplanets—those beyond our solar system—the question has been transformed from a science-fiction trope to one discussed in scientific journals and conferences.
And it quickly leads to another question: How did life start here on Earth? That question, says Dimitar Sasselov, professor of astronomy and director of the Origins of Life Initiative at Harvard, “is one of the big unsolved questions humanity has always asked.” And yet for various reasons it has been difficult to answer. Biology has been very good at describing how living organisms work; it has been far less successful at answering what life is and how it could emerge from a non-living world.