Despite knowing when life first appeared on Earth, scientists still don’t understand how it happened, which has important implications for the likelihood of finding life elsewhere in the universe. Now, a new study by researchers at Columbia University shows using a statistical technique called Bayesian inference how complex extraterrestrial life could evolve on alien worlds.
“The rapid emergence of life and the late evolution of humanity, in the context of the evolutionary timeline, are certainly suggestive. But in this study it is possible to really quantify what the facts tell us,” explains David Kipping. , leader of the work that publishes the journal Proceedings of the National Academy of Sciences.
We know from the geological record that life began relatively quickly, as our planet’s environment was stable enough to support it. We also know that the first multicellular organism, which led to our current civilization, took much longer to evolve, approximately 4 billion years.
Our searches within the solar system have yielded no direct evidence of extraterrestrial life, and remote sensing of chemical biomarkers on exoplanets is years ahead of the observational capabilities we have today.
So Kipping used the chronology of the first tests of life and the evolution of mankind wondering how often we would expect life and intelligence to rise again if Earth’s history repeated itself, rerunning the clock over and over. time. He framed the problem in terms of four possible answers:
- life is common and often develops intelligence
- life is rare but often develops intelligence
- life is common and rarely develops intelligence
- life is rare and rarely develops intelligence
This Bayesian statistical inference method, used to update the probability of a hypothesis as evidence or information becomes available, establishes prior beliefs about the system being modeled, which are then combined with data to produce probabilities of outcomes.
“The technique is similar to betting odds,” says Kipping. “It encourages repeated testing of new evidence against your position, essentially a positive feedback loop to refine your estimates of the probability of an event.”
And what have been the results?
The analysis is based on evidence that life arose within 300 million years of the formation of Earth’s oceans as found in carbon-13-depleted zircon deposits, a very rapid start in the context of the life on Earth.
This means that if planets with Earth-like conditions and evolutionary timelines are common, then the analysis suggests that life should have little trouble spontaneously emerging on other planets. And what are the chances that this life can be complex, differentiated and intelligent? There is only a 3: 2 chance of finding intelligent life, which comes down to 40%. Which clearly suggests that it is neither an easy nor a safe process.
“If we replay Earth’s history, the emergence of intelligence is actually somewhat unlikely,” Kipping said, further noting that the odds in the study are not overwhelming, they are very close to 50:50, and the findings they should be treated as a simple push towards a hypothesis, without certainties or guarantees.
“Encouragingly, however, the case of a universe full of life emerges as the favorite bet. Humanity should not be discouraged in the search for intelligent life on worlds beyond Earth,” concludes Kipping.
Referencia: David Kipping, An objective Bayesian analysis of life’s early start and our late arrival, Proceedings of the National Academy of Sciences (2020). DOI: 10.1073/pnas.1921655117
