We’re currently the only planet that we know of in the entire universe that supports and harbors life. So, in a sense, the best way to explore what other habitable worlds might look like is to understand more about our own.
That’s what researchers set out to do in a new study that simulated what Earth would look like if life never developed. Their findings, published in The Planetary Science Journal and flagged by ScienceAlert, could help astronomers distinguish which atmospheric signatures they see on other worlds can be independent of life — and which ones can only be explained by its presence.
“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,” said lead author Samantha Gilbert-Janizek, an astronomer at UC Riverside, in a statement about the work.
The research, crucially, also explores whether our planet would still maintain its habitability without life ever intervening.
In the study, the researchers built a computer model based on the planet’s geochemical systems, using physical factors like the properties of its core, the movement of its crusts and its oceans, and how it would all affect the exchange of chemicals between the core up to the surface of the planet and atmosphere. In all, they incorporated 19 different non-biological properties of a rocky planet and used it to simulate how Earth evolved over five billion years.
Perhaps not so flatteringly to lifeforms, the Earth didn’t change too much without us around and stayed more than habitable. The oceans still held a similar amount of water, and surface temperatures stayed well within a comfortable range.
The most significant deviation was the absence of atmospheric oxygen, which isn’t surprising. Around three billion years ago, cyanobacteria known as blue-green algae helped pump the atmosphere full of oxygen, and so an oxygen-rich atmosphere may be an example of something that requires the emergence of life. Still, when looking for habitability in astronomy, oxygen is an ancillary concern compared to the presence of liquid water.
More on biology: We Were Totally Wrong About How Life on Earth Started, Study Suggests
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