A new computer simulation of a lifeless Earth provides astronomers with a critical baseline to help distinguish between planets that are merely habitable and those that are actually inhabited.
Researchers at the University of Washington developed the model to simulate how a rocky planet’s atmosphere and surface evolve through purely geological and chemical processes, without the influence of biology.
Simulating five billion years of evolution
The research, published September 18, 2026, in The Planetary Science Journal, tracks the movement of chemicals across five interconnected systems: the core, mantle, crust, surface, and atmosphere.
Lead author Dr. Samantha Gilbert-Janizek, a postdoctoral fellow at UC Riverside who conducted the research as a doctoral student at the University of Washington, ran the simulation from Earth’s formation 4.5 billion years ago through 500 million years into the future. The result was a world that remained habitable, possessing both oceans and an atmosphere, but lacked biological life.
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,
Dr. Samantha Gilbert-Janizek
Dr. Gilbert-Janizek expanded this framework to include the surface and atmosphere, creating a more comprehensive geochemical account.
Establishing a scientific null hypothesis
The primary utility of the model is to address the “false-positive” problem in astrobiology. Many gases associated with life, such as methane or oxygen, can also be produced by geological activity, UV photochemistry, or other non-biological processes. For example, non-biological methane production can occur through serpentinization, where rocks like peridotite react with water.
By providing a validated abiotic baseline, the tool allows researchers to see if the atmosphere of a distant exoplanet can be explained by physics and geology alone. If a telescope’s observations of a planet do not match the simulation’s results, it increases the likelihood that life is present and altering the environment. However, a mismatch alone would not serve as conclusive proof of life’s existence.
The simulation’s geochemical states can be processed through radiative transfer codes, such as PICASO, to generate synthetic spectra. These spectra mimic what a telescope would observe when looking at a lifeless but habitable Earth.
The researchers generated reflected-light spectra from 0.2 to 2.0 micrometers under specific conditions, including a 50% cloud-cover weighting, a 90-degree phase angle, and a spectral resolution of R=140. Even in this lifeless model, the spectra show clear absorption bands for carbon dioxide and water vapor.
Validating the planetary model
To ensure accuracy, the team tested the simulation against 19 independent planetary parameters. The model successfully reproduced the properties of pre-industrial Earth, including surface temperature, ocean mass, and heat flow through the mantle. Of the 19 benchmarks, 17 fell within the uncertainty range of the targets. The remaining two differed by approximately two standard deviations (2σ), assuming a normal distribution.
| Metric | Model Result / Comparison |
|---|---|
| Simulation Duration | 5 billion years |
| Benchmarks Matched | 17 of 19 within error margin |
| Mean Surface Temperature | 286.9 K |
The simulation tracks 19 non-biological properties, such as the amount of heat a planet receives from its star and the outflow of gases from the subsurface. The model’s findings suggest that life may not be necessary to maintain habitable surface conditions over long periods, noting that the carbonate–silicate cycle can regulate greenhouse gas concentrations via surface silicate weathering.
The simulation relies on several assumptions, including that abiotic methane production is not a major climate driver and that plate tectonics remain active.
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Future observations with HWO and JWST
The model is intended to support data collection from current and future space missions. This includes spectroscopic observations from the James Webb Space Telescope (JWST) and NASA’s planned Habitable Worlds Observatory (HWO). The HWO is currently in pre-formulation development, with a concept review expected in the late 2020s and a launch anticipated in the 2040s.
Because the synthetic spectra generated by the model already cover the 0.2 to 2.0 micrometer wavelength range planned for the HWO, researchers can use it to tailor a null hypothesis to specific worlds. This helps distinguish between planets that have conditions suitable for life and those that are actually inhabited.
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, University of Washington, as reported by Space.com