Earth's history could be used to spot plant life on alien worlds

Earth’s natural history may now serve as a guide for astronomers to spot exoplanets. About 500 million years ago, this planet had a different light signature due to the dominance of moss. About 300 million years ago, ferns dominated and mature plant forms rule today - strengthening our planet’s light signature (Jack O'Malley-James/Wendy Kenigsberg/Brand Communications).

Earth's history could be useful to help spot planets where vegetation may exist, potentially showing signs of life, new research says.

The new study, published by researchers from Cornell University, details something they call a "template for vegetation fingerprints" to figure out the age of potentially habitable exoplanets.

“Our models show that Earth’s vegetation reflectance signature increases with coverage of our planet’s surface, but also with the age of our planet,” said co-author Jack O’Malley-James, research associate in astronomy at Cornell’s Carl Sagan Institute, in a statement.

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The study was published in the Astrobiology Journal.

Lisa Kaltenegger, an astronomer at Cornell, said that the Earth's history is "key" for finding life in the universe and the way plants evolved could be helpful to finding life elsewhere.

“We use Earth’s history as a key for finding life in the universe,” Kaltenegger said in the statement. “Our work shows that as plants evolved on Earth, the vegetation signal that reveals their presence became stronger, making older exoplanets really interesting places to look for vegetation.”

The study looked at how the planet's vegetation red edge [VRE] ("often cited as a spectral biosignature for surface vegetation on exoplanets," according to the abstract) would look over time when viewed from outer space as it evolved.

"Early plants such as mosses and liverworts, which dominated the land 500–400 million years ago, produce a weaker VRE, approximately half as strong as that of modern vegetation," the abstract says.

But as time has gone on, VRE gets stronger, potentially an indicator of life. "Our findings suggest that older and hotter Earth-like planets are good targets for the search for a VRE signature. In addition, hot exoplanets and dry exoplanets with some water could be the best targets for a successful vegetation biosignature detection," the abstract says.

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It's possible that as Earth continues to become warmer due to the effects of climate change, the VRE signal could become stronger, making it easier to find life among exoplanets.

“Observing an exoplanet is more challenging, but telescope technology is getting better at spotting tiny signals,” said O’Malley-James. “And factoring Earth’s changing landscapes into our models will make it easier to detect vegetation in the future on other worlds.”

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