Scientists build a lifeless Earth to help spot real alien life
A University of Washington team modeled 5 billion years of Earth's chemistry with no biology at all, giving astronomers a baseline for telling a truly inhabited planet from one that only looks that way.
Astronomers at the University of Washington have built a computer model of Earth that strips out every living thing, from microbes to forests, to see what the planet's chemistry would look like on its own. The team announced the work on Monday, saying the simulation is meant to help astronomers reading the atmospheres of distant worlds avoid mistaking ordinary geology for signs of life.
The study, led by Samantha Gilbert-Janizek, a former UW doctoral student now a postdoctoral fellow at UC Riverside, with UW astronomy professor Rory Barnes as senior author, was published last month in The Planetary Science Journal. It couples models of Earth's core, mantle, crust, surface and atmosphere into a single system running from 50 million years after the planet's formation to roughly 500 million years into the future. With no biology included, the model still reproduced 19 measured properties of the pre-industrial Earth — among them atmospheric carbon dioxide and water vapor, surface temperature and ocean mass — within the uncertainty of actual measurements.
Why a dead Earth matters
More than 6,000 planets have now been cataloged beyond the solar system, and a future instrument, NASA's planned Habitable Worlds Observatory, is meant to directly image rocky planets around sun-like stars and study their atmospheres for chemical traces of life. The risk scientists want to avoid is a false positive: a planet whose oxygen or other gases built up through ordinary rock chemistry, stellar radiation or volcanic activity, with no organisms involved. "This model can help us see how habitable but non-living planets might mimic living planets," Gilbert-Janizek said.
Barnes said matching the model to Earth's known history was the critical test: "That calibration gives us confidence that future simulations of exoplanets will be accurate." Independent coverage of the paper noted the model rests on assumptions about Earth's early history that could shift its predictions for planets with very different pasts. The research was funded by NASA.
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