Life finds a way, especially when it comes to Jurassic worlds. Clever Cornell University astronomers have made a discovery that could significantly advance the search for signs of extraterrestrial life on planets orbiting distant stars. Their research, which delves into Earth’s evolutionary history over the past 540 million years, reveals that telescopes could better detect potential chemical signatures of life on Earth-like exoplanets that resemble the conditions during the time of the dinosaurs.
The key to this discovery lies in what scientists call “biosignature pairs.” These pairs consist of gases such as oxygen and methane, and ozone and methane. These gases, when found together, could indicate the presence of life on a planet. According to researchers, these biosignature pairs were more pronounced in Earth’s atmosphere approximately 100 million to 300 million years ago, when oxygen levels were significantly higher.
“Modern Earth’s light fingerprint has been our template for identifying potentially habitable planets, but there was a time when this fingerprint was even more pronounced – better at showing signs of life,” says study co-author Lisa Kaltenegger, director of the Carl Sagan Institute (CSI) and associate professor of astronomy in the College of Arts and Sciences (A&S), in a university release. “This gives us hope that it might be just a little bit easier to find signs of life – even large, complex life – elsewhere in the cosmos.”
Scientists used climate models known as GEOCARB and COPSE to simulate Earth’s atmospheric composition and resulting transmission spectra over five 100-million-year increments of the Phanerozoic. This period includes significant changes as the Earth’s biosphere diversified, forests grew, and complex life forms like dinosaurs emerged.
“It’s only the most recent 12 percent or so of Earth’s history, but it encompasses pretty much all of the time in which life was more complex than sponges,” explains study co-author Rebecca Payne, research associate at CSI. “These light fingerprints are what you’d search for elsewhere, if you were looking for something more advanced than a single-celled organism.”
While it’s uncertain whether similar evolutionary processes occur on exoplanets, Payne and Kaltenegger believe their models provide valuable insight into what a Phanerozoic-era Earth would look like to a telescope. This information allows scientists to create new templates for habitable planets with varying levels of atmospheric oxygen.
Kaltenegger, who pioneered the modeling of Earth’s appearance to distant observers based on geological and atmospheric changes over time, notes that these models serve as our “ground truth” for identifying potential evidence of life on other worlds.
To date, about 35 rocky exoplanets have been discovered within habitable zones where liquid water could exist. Analyzing the atmospheres of these exoplanets, a capability made possible by NASA’s James Webb Space Telescope, is now within reach. However, scientists need to know what to look for. The models developed by Kaltenegger and Payne identify planets resembling Phanerozoic Earth as the most promising candidates for finding life in the universe.
These models also open the door to a tantalizing possibility – that if a habitable exoplanet is found with an atmosphere containing 30 percent oxygen, life there might not be limited to microscopic organisms but could include larger and more diverse creatures reminiscent of the megalosauruses or microraptors that once roamed Earth.
“If they’re out there, this sort of analysis lets us figure out where they could be living,” concludes Payne.
The study is published in the journal Monthly Notices of the Royal Astronomical Society Letters.