In the search for life in the Universe, Earth provides a template of evolution for the one habitable planet we know. Earth’s atmospheric composition has changed significantly throughout its history. The last 500 million years — the Phanerozoic Eon, which includes the origins of animals, dinosaurs, and land plants — saw oxygen rise from around 10% to 35%. But the resulting transmission spectra are a crucial missing piece in our search for signs of life in exoplanet atmospheres. In a new study, astronomers modeled the atmospheric composition and transmission spectra of five stages in Earth’s Phanerozoic Eon. Two key biosignature pairs — oxygen and methane, and ozone and methane — appeared stronger in models of Earth roughly 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,” said Dr. Lisa Kaltenegger, director of the Carl Sagan Institute.
“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.”
Using estimates from two established climate models (GEOCARB and COPSE), Dr. Kaltenegger and Cornell University astronomer Rebecca Payne simulated Earth’s atmospheric composition and resulting transmission spectra over five stages (approximating 500, 400, 300, 200, and 100 million years) of the Phanerozoic Eon.
Each features significant changes as a complex ocean biosphere diversified, forests proliferated and terrestrial biospheres flourished, influencing the mix of oxygen and other gasses in the atmosphere.
“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,” Dr. Payne said.
“These light fingerprints are what…
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