A find by American researchers suggests that between 300 and 100 million years ago, extraterrestrial beings may have found it significantly easier to detect life on Earth. This intriguing deduction is outlined in the journal Monthly Notices of the Royal Astronomical Society: Letters, and is based on models.
Methodology
Using these models, the researchers first examined the state of Earth’s atmosphere over the past 540 million years. They specifically studied the atmospheric concentration levels of oxygen, ozone, and methane, elements that, when detected together in a planet’s atmosphere, strongly indicate the presence of life. With the concentrations of these elements established, the researchers then took one step further. They hypothesized what the telescopes we currently use to assess the livability of distant exoplanets would have observed if they had been observing Earth from a distance at any point during the past 540 million years. The crucial question to be answered was whether these telescopes would have been capable of detecting these life-indicating concentrations of oxygen, ozone, and methane – and thus life on Earth itself.
Results
The research yielded breath-taking results. The models hint that the presence of life was demonstrated more unequivocally through the atmospheric concentrations of oxygen, methane, and ozone 300 and 100 million years ago than it is now. This suggests that it may be significantly more challenging for extraterrestrial beings to detect life on Earth today, whereas it may have been much easier 300 and 100 million years ago.
According to the researchers, aliens witnessing our planet from a distance today could conclude from the presence of oxygen (or ozone) and methane that there is life on Earth. However, for this research, the scientists examined how the atmospheric signal of life has transformed over time, leading to a fascinating conclusion.
A Clearer Signal
They found that these biosignature pairs of oxygen, ozone, and methane were also detectable hundreds of millions of years ago. And perhaps even more exciting, in certain historical periods, such as the Jurassic period when there was far more oxygen in the atmosphere than there is today, these signals would have been much clearer. Essentially, this indicates that it would have been much easier for potential extraterrestrial life to identify life on Earth during the era of the dinosaurs through the study of Earth’s atmosphere.
300 and 100 Million Years Ago
Delving deeper, the models reveal that Earth’s atmosphere testified to the existence of life more clearly 300 million and 100 million years ago than it does today. “Three hundred million years ago, this was due to the evolution of trees which led to the formation of forests on the continents for the first time,” explains researcher, Payne. “This resulted in the production of unparalleled amounts of oxygen. And again, 100 million years ago – when the dinosaurs roamed Earth – the supercontinent Pangea split apart leading to changes in the continents which temporarily increased the oxygen concentration.”
Implications
The idea that life on Earth once had a much more significant impact on the Earth’s atmosphere is fascinating. Yet, it also has implications for our search for life on other planets. We currently know of approximately 40 rocky extraterrestrial worlds which could potentially harbor liquid water. Therefore, it’s only a matter of time before James Webb telescopes explore their atmospheres in search of biosignatures.
However, there’s an important takeaway from Payne’s research: it’s crucial that we don’t focus solely on a single biosignature, but look for combinations of these. The research emphasizes that the perfect livable planet does not exist and suggests that in our search for extraterrestrial life, we need to focus more on planets that resemble the Earth during the time of the dinosaurs.
Extraterrestrial Dinosaurs?
Payne and his colleague, Kaltenegger, underscore that this approach could make it easier to find convincing evidence of life. “Hopefully, we are going to find some planets that have more oxygen in their atmosphere than Earth currently does, because that could simplify the search for life,” adds Kaltenegger. “Who knows, maybe we’ll also find dinosaurs waiting for discovery.”
While this last comment is clearly made in jest, the research subtly suggests that a planet with an atmosphere very different from that of present-day Earth could still harbor very interesting life forms. History has shown that a planet with an atmosphere comprised of 30 percent oxygen is not merely habitable for microbes, but may be particularly well-suited to very large organisms.
“Large multicellular life forms on Earth evolved and diversified enormously once the oxygen concentration was high enough,” Payne notes. “Many big and complex life forms, like humans, require high oxygen levels to survive. There’s also research indicating that a high amount of oxygen in the atmosphere is necessary to support organisms as large as dinosaurs and to meet the energy requirements of these huge bodies. It’s a complex story, but it’s certainly possible that a world with a lot of oxygen is home to large and complex life forms.”
