Scientists at Cornell University suggest that by examining Earth’s Phanerozoic era, telescopes could improve the detection of potential signs of life on exoplanets
By examining the last 540 million years of Earth’s evolution, using the Phanerozoic Eon, researchers from Cornell University have determined that telescopes could enhance their ability to detect potential chemical signs of life in the atmosphere of an Earth-like exoplanet. This exoplanet would more closely resemble the environmental conditions of the era when dinosaurs existed rather than the present day.
A growing discovery
The analysis focused on two crucial biosignature pairs—oxygen and methane and ozone and methane. These pairs exhibited stronger signals in models of Earth approximately 100 million to 300 million years ago, a period marked by significantly higher oxygen levels.
The models simulated transmission spectra, also known as the light fingerprint, generated by an atmosphere that absorbs certain colours of starlight while allowing others to pass through. This information is essential for scientists to determine the composition of the atmosphere.
“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,” said Lisa Kaltenegger, director of the Carl Sagan Institute (CSI) and associate professor of astronomy. ”
A telescope’s view
The scientists utilised data from two well-established climate models, GEOCARB and COPSE, to simulate the atmospheric composition of Earth and the resulting transmission spectra. This simulation covered five successive 100-million-year intervals of the Phanerozoic, each marked by substantial changes.
These changes coincided with the diversification of a complex ocean biosphere, the proliferation of forests, and the flourishing of terrestrial biospheres. These biological events significantly influenced the atmosphere’s composition, particularly regarding oxygen and other gases.
“It’s only the most recent 12% or so of Earth’s history, but it encompasses pretty much all of the time in which life was more complex than sponges,” said Payne.
“These light fingerprints are what you’d search for elsewhere, if you were looking for something more advanced than a single-celled organism.”
Whether exoplanets undergo similar evolutionary processes remains uncertain. According to Payne and Kaltenegger, their models complete a missing puzzle piece, offering insights into how a Phanerozoic era might appear when observed through a telescope. These models establish new templates for habitable planets with diverse atmospheric oxygen levels.
Telescopic capabilities and the James Webb space telescope
Approximately 35 rocky exoplanets have been identified within habitable zones capable of sustaining liquid water, as noted by Kaltenegger. Examining an exoplanet’s atmosphere, if present, pushes the boundaries of the technical capabilities of NASA’s James Webb Space Telescope but has become feasible.
However, the researchers emphasise the importance of knowing what to look for. According to their models, planets resembling the Phanerozoic Earth are considered the most promising targets in the quest for extraterrestrial life.
These models allow scientists to contemplate a purely theoretical scenario. If a habitable exoplanet possesses an atmosphere with 30% oxygen, life there may not be restricted to microorganisms. Instead, it could include creatures as large and diverse as the megalosaurs or microraptors that once inhabited Earth.
