In the quest to identify signs of life beyond our solar system, scientists have traditionally relied on Earth as a model, being the only known haven for life. However, recent research suggests that a bygone era in Earth’s history may serve as a more effective reference point for detecting complex life in the universe than our present-day environment.
Conventional telescopes designed to assess the habitability of exoplanets typically seek biosignatures in extraterrestrial atmospheres, drawing comparisons with the compounds and compound levels found in today’s Earth. Nevertheless, researchers propose that these telescopes might have a greater chance of identifying distinctive signs of life on planets that do not closely resemble the contemporary Earth. Instead, the focus could shift to celestial bodies resembling Earth during a distant epoch when dinosaurs roamed the land. The rationale behind this lies in the fact that during that ancient period, Earth hosted higher oxygen levels. In simpler terms, detecting abundant oxygen on an exoplanet may prove more feasible than identifying trace amounts of the gas.
Lisa Kaltenegger, co-author of the study and director of the Carl Sagan Institute, noted, “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. 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.”
Scientific consensus acknowledges that the oxygen levels in Earth’s atmosphere have fluctuated over the past 400 million years, oscillating between 16 percent, just sufficient to ignite a fire, and as high as 35 percent, beyond which fires would have been perpetually unquenchable. Approximately 50 million years ago, oxygen levels stabilized at the familiar 21 percent observed today.
Crucially, the study’s models indicate that around 300 million years ago, oxygen levels peaked at 30 percent, creating conditions conducive to the development of complex life forms. This includes the era dominated by dinosaurs, spanning roughly from 245 million to 66 million years ago.
Consequently, scientists suggest that telescopes could potentially identify exoplanets resembling Earth during their own Phanerozoic era. Such planets would boast atmospheres rich in oxygen, akin to Earth during that period, and likely exhibit distinctive pairs of biosignatures, such as oxygen and methane, as well as ozone and methane. These combinations are readily discernible through telescopic observation, according to the findings of the new study.
Rebecca Payne, the lead author of the study and a scientist at Cornell University, emphasized the significance of the Phanerozoic era, which represents only the most recent 12% of Earth’s history but encompasses the vast majority of the time during which life evolved beyond simple microbes and sponges. “These light fingerprints are what you’d search for elsewhere if you were looking for something more advanced than a single-celled organism,” Payne noted.
The prospect of identifying exoplanets with atmospheres boasting 30 percent oxygen levels is particularly intriguing for scientists. Such a finding could indicate the potential existence of life forms beyond microscopic organisms, raising the possibility of “creatures as large and varied as the megalosauruses or microraptors that once roamed Earth.”
Lisa Kaltenegger expressed optimism about the search for planets with higher oxygen levels than present-day Earth, stating, “Hopefully, we’ll find some planets that happen to have more oxygen than Earth right now because that will make the search for life just a little bit easier.” She added, with a touch of anticipation, “And, who knows, maybe there are other dinosaurs waiting to be found.”
Details of this research are outlined in a paper published in October in the journal Monthly Notices of the Royal Astronomical Society.
- Detecting alien life might be easier if we hunt for ‘Jurassic worlds.’ Here’s why – Space.com
- Oxygen bounty for Earth-like exoplanets: spectra of Earth through the Phanerozoic – Monthly Notices of the Royal Astronomical Society
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