Scientists Simulate Lifeless Earth to Find Exoplanet Biosignatures

Researchers have built a virtual version of Earth that lacks any life to help astronomers determine whether atmospheric gases detected on distant exoplanets truly indicate biological activity.

Simulating Five Billion Years Without Biology

Published on September 18, in The Planetary Science Journal, the study outlines a computer model that tracks Earth’s geochemical evolution across five billion years, starting from its formation 4.5 billion years ago up to 500 million years into the future. Samantha Gilbert-Janizek of the University of Washington, now based at UC Riverside, developed the simulation, as Space.com reported.

The new model expands upon earlier work by Rory Barnes at the University of Washington, which simulated a planet’s core, mantle, and crust. Gilbert-Janizek integrated the surface and atmosphere into the framework to track how chemicals move across five interconnected systems according to The Times of India. Despite omitting biological processes entirely, the simulation successfully reproduced 19 key properties of pre-industrial Earth, such as ocean mass, surface temperature, and heat flow noted ThePrint. The simulation tracks 19 distinct properties of a rocky planet that have no relation to life, including the heat a planet receives from its star, the exchange of heat and chemicals running from the core to the surface, and the subterranean outflow of specific gases. During testing against target values for pre-industrial Earth, 17 items fell directly within the estimated uncertainty range of the targets, while the remaining two differed by only about two standard deviations assuming a normal distribution.

The simulation simultaneously incorporates the planet’s core, mantle, surface, and atmosphere, reproducing observations of pre-industrial Earth within estimated measurement uncertainties. The research was announced separately by the University of Washington on November 2, explaining how the model helps astronomers differentiate between planets with conditions suitable for life and those containing living organisms.

The University of Washington’s announcement noted that the model successfully reproduced 19 key observations of pre-industrial Earth within estimated measurement uncertainties, including heat flow through the mantle.

The project builds on prior models from the laboratory of astronomy professor Rory Barnes, which previously included Earth’s interior and stellar radiation effects but omitted the surface and atmosphere. Gilbert-Janizek expanded the model by including these additional systems to construct a more complete representation of the planet.

When we interpret observations of an exoplanet’s atmosphere, this tool will help us determine the probability that what we observe indicates life on the surface,

Samantha Gilbert-Janizek, Lead Author

Astronomers have cataloged more than 6,000 planets beyond the solar system according to EurekAlert!, focusing on rocky worlds that may harbor liquid water. However, finding a habitable environment does not confirm the presence of living organisms. Many gases associated with biological activity can also be generated through natural geological processes reported Tech Times.

Geological processes, heat originating from a planet’s interior, and radiation from its host star can all influence atmospheric composition, requiring scientists to understand non-biological processes before identifying signs of life.

The model also operates on specific assumptions, such as treating abiotic methane production as a non-major climate driver, whereas non-biological methane can emerge from serpentinization where rocks like peridotite react with water. The study demonstrates one of many potential evolutionary pathways rather than proving Earth would have necessarily remained habitable without life.

Testing Exoplanet Atmospheres Against a Null Hypothesis

The plug-and-play simulation allows researchers to input the bulk properties of an exoplanet and run the model to generate synthetic reflected-light spectra noted Universe Today. If the resulting abiotic atmosphere matches what telescopes observe, the real planet likely lacks life stated Around Prague.

If the observations deviate from the lifeless model, the world becomes a candidate for follow-up studies reported Space.com. By adjusting initial parameters such as planetary mass, stellar irradiance, interior composition, and water inventory, the team can construct abiotic baselines for rocky exoplanets that differ from Earth in systematically varied ways.

The synthetic spectra cover the wavelength range planned for NASA’s Habitable Worlds Observatory, as well as observations by the James Webb Space Telescope and future ground-based telescopes with mirrors exceeding 30 meters detailed Tech Times. The model showed that a lifeless Earth can maintain liquid-water oceans for billions of years, though it lacks abundant atmospheric oxygen reported ScienceAlert. This outcome contributes to debates surrounding the Gaia hypothesis by suggesting that life and long-term planetary habitability can be decoupled noted ScienceAlert.

To generate these synthetic views, the geochemical states are fed into radiative transfer codes such as PICASO, which calculates the absorption and scattering of light in an atmosphere. Reflected-light spectra from 0.2 to 2.0 micrometers were generated under conditions including a 90-degree phase angle, 50% cloud-cover weighting, and a spectral resolution of R=140.

Comparing these synthetic spectra reveals that even a lifeless Earth displays clear absorption bands originating from water vapor and carbon dioxide. Through carbonate-silicate cycling driven by silicate weathering at the surface, the simulation regulates greenhouse gas concentrations over long timeframes without requiring biological feedbacks for climate regulation.

After more than a decade of work by many scientists, Dr. Gilbert-Janizek has finally completed a model of the Earth that simultaneously reproduces properties of Earth’s core, mantle, surface and atmosphere. That calibration gives us confidence that future simulations of exoplanets will be accurate.

Rory Barnes, Senior Author

This newfound ability to model such complex planetary systems provides a vital foundation for understanding the potential habitability of worlds beyond our own.

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