Scientists have built a computer model of Earth without life to help determine whether distant planets could host living organisms or merely have conditions that resemble those of an inhabited world.Researchers at the University of Washington developed a simulation that models how chemicals move between a planet’s core, mantle, crust, surface and atmosphere over billions of years. The model could help astronomers identify atmospheric signals on rocky exoplanets that cannot be explained by geological and other non-biological processes.The distinction matters as scientists search for signs of life beyond our solar system. Astronomers have cataloged more than 6,000 exoplanets and are examining the atmospheres of promising worlds for gases that could indicate biological activity. However, finding a potentially habitable planet does not establish that life exists there.To address this challenge, the researchers simulated Earth’s geochemical evolution over five billion years, covering its formation around 4.5 billion years ago and extending roughly 500 million years into the future. The model excludes the influence of living organisms, allowing scientists to examine how a planet’s systems could evolve without biology.Simulating a lifeless EarthThe simulation builds on an earlier model developed in the laboratory of Rory Barnes, an associate professor of astronomy at the University of Washington. Previous versions included the planet’s core, mantle, crust and stellar radiation but did not account for the surface and atmosphere.Lead author Samantha Gilbert-Janizek expanded the model to include those missing systems, creating a more complete picture of how chemicals move throughout a rocky planet. The simulation reproduced 19 planetary properties, including heat flow through Earth’s mantle.The model provides a baseline for understanding what a planet’s atmosphere might look like without life. Researchers can adjust its inputs to represent other rocky exoplanets and test whether their observed atmospheric conditions can be reproduced through non-biological processes.This could help scientists avoid mistaking geological activity for evidence of extraterrestrial organisms. A planet might have an atmosphere containing chemicals associated with life, but those gases could also arise from interactions between its interior, surface and atmosphere.Distinguishing life from geologyEarth offers an example of why this distinction is important. Living organisms continually release gases such as oxygen and methane into the atmosphere. These gases react with one another, so their simultaneous presence can suggest that biological processes are replenishing them.An astronomer observing Earth from another star system might therefore consider the combination a possible sign of life. But scientists first need to understand whether non-biological processes could produce similar atmospheric conditions on other worlds.The new model allows researchers to test that possibility. If a planet’s observed atmosphere can be reproduced without including life, the findings may offer a non-biological explanation. If the simulation cannot reproduce the observations, the planet could become a more interesting target for further investigation.The researchers say the work could also inform the design of future space telescopes, including NASA’s proposed Habitable Worlds Observatory, which is intended to study potentially habitable planets around other stars.The study does not identify an inhabited exoplanet or detect extraterrestrial life. Instead, it provides a tool for improving how scientists interpret atmospheric observations and distinguish potentially biological signals from the natural evolution of a planet.The study appears in The Planetary Science Journal.