A far-away planet covered in dinosaurs could be easier to spot than one full of intelligent aliens.
That’s the conclusion of a new study from Cornell University into the telltale signs of extraterrestrial life.
When searching for life in the universe, astronomers look for ‘light fingerprints’ or biosignatures in a planet’s atmosphere, indicators of the conditions that may allow life to emerge.
Abundant oxygen is one of the most important.
Now, researchers modelling Earth’s own biosignature over time have found two key biosignature pairs – oxygen and methane, and ozone and methane – were much stronger 100 million to 300 million years ago, during the time of the dinosaurs.
During this time oxygen was significantly higher, around 30% – still firmly in the sweet spot, or ‘fire window’, of 16% to 35%.
Fires are important to natural cycles, and below 16%, they cannot ignite.
Above 35%, they cannot be extinguished.
Today the percentage is about 21%, meaning any alien civilisations trying to determine if life exists on Earth would have found it significantly easier during the time of the dinosaurs than today.
And it works both ways, meaning the conditions that gave rise to the dinosaurs, if replicated elsewhere, would give off strong telltale signs to astronomers searching for life.
‘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 co-author and associate professor Lisa Kaltenegger, director of the Carl Sagan Institute (CSI).
Together with first author Dr Rebecca Payne, research associate at CSI, Associate Professor Kaltenegger used established climate models to simulate Earth’s atmospheric composition working backwards in time.
The pair found that as the planet’s complex biosphere diversified, with plants and trees spreading across the land, the percentage of oxygen increased.
‘The Phanerozoic is just the most recent 12% or so of Earth’s history, but it encompasses nearly all of the time in which life was more complex than microbes and sponges,’ said Dr Payne, an astrobiologist and geologist.
‘These light fingerprints are what you’d search for elsewhere, if you were looking for something more advanced than a single-celled organism.’
Astronomers have already identified about 40 rocky exoplanets in habitable zones around stars where life could exist, and Nasa’s James Webb Space Telescope has already proved capable of measuring biosignatures.
Now, it can also be used to search for planets with atmospheres more like Phanerozoic Earth.
‘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,’ said Associate Professor Kaltenegger.
‘And who knows, maybe there are other dinosaurs waiting to be found.’
The study is published in the journal Monthly Notices of the Royal Astronomical Society: Letters.
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