How Earth’s early oceans and atmosphere help guide the search for life beyond

Life and life-sustaining environments, including oceans, have existed on a dynamic Earth for more than four billion years despite the multitude of challenges that come with stellar, solar system, and planetary evolution. Each of our many past planetary states, or alternative Earths, was associated with a particular atmospheric composition, and those atmospheres contained gases such as oxygen and methane that were produced by early life. Using ancient Earth to understand when and how these biosignature gases accumulated is allowing us to select targets and techniques for exploring the many Earth-like planets beyond our solar system. Further, Earth scientists and prebiotic chemists are working together in new ways to understand how and where life first emerged. This new perspective could also help guide the search for life elsewhere in the solar system and far beyond.

This presentation is about the coevolution of life and its environments on Earth over billions of years, touching on key evolutionary innovations, the steps and dynamics of biospheric oxygenation, potential tectonic controls, and nutrient cycling—among other first-order patterns and drivers. The focus will include biosignatures emphasizing early Earth and its relevance in the search for life on exoplanets. Among the many lessons learned, early Earth has taught us about false negatives—that is, the possible absence of detectable atmospheric biosignatures above an ocean brimming with life. Overall, however, the evolution of life and its ecological impacts are direct reflections, through cause-and-effect relationships, of the chemical and physical evolution of solid and surficial Earth.