If an alien species were scouring the Galaxy for habitable worlds, the land of the dinosaurs could be easier to spot than a planet of modern-day humans, a study has found.
When searching for potentially inhabited exoplanets, astronomers look for various chemical imbalances in the atmosphere that are only possible with the help of biological processes.
These are known as biosignatures, and could help discover life on distant planets beyond our Solar System.
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Discovering Earth as an exoplanet
What would Earth look like to a distant, alien observer? And if they decided to to a spectral reading of our atmosphere, what chemicals would they find?
Earth’s atmosphere currently contains 20% oxygen and only traces of carbon dioxide.
Without plant life breaking down carbon dioxide and releasing it as oxygen, this ratio would be very different.
This means an intelligent civilisation elsewhere in the Galaxy could potentially use this ratio to identify our planet’s habitability.
This is one of the things that makes a planet habitable.
But the level of oxygen in our atmosphere hasn’t remained constant in the last 540 million years that large complex creatures have roamed its surface.
Discovering a 'dinosaur' planet
A team of astronomers investigating which era might be the most detectable found that around 300 million years ago, our planet’s oxygen reached a peak of 30%, just in time for the dinosaurs to evolve.
"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 Lisa Kaltenegger from Cornell University, who led the study.
"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."
Read the full paper Oxygen bounty for Earth-like exoplanets: spectra of Earth through the Phanerozoic by R C Payne, L Kaltenegger.
