A new model has shown that humanity might not be exceptional but instead a natural result of evolution on our planet—and possibly on others as well.
The model deposes the “hard steps” theory, which argues that intelligent life was a majorly improbable event. In fact, it may not have been all that extraordinary.
A team of researchers at Penn State, who led the work, suggested that it increases the chances of intelligent life existing elsewhere in the universe. Odds are, we are not alone here.
“This is a significant shift in how we think about the history of life,” said Jennifer Macalady, a co-author of the study and a professor of geosciences at Penn State.
“It suggests that the evolution of complex life may be less about luck and more about the interplay between life and its environment, opening up exciting new avenues of research in our quest to understand our origins and our place in the universe.”
The “hard steps” theory was developed in 1983 by theoretical physicist Brandon Carter. It states that the evolutionary origin of humans was highly unlikely due to the time it took for us to evolve on Earth, based on the sun’s total lifespan being 10 billion years and the Earth’s age of around five billion years. Therefore, the likelihood of other intelligent civilizations beyond Earth is extremely low.
In the new study, the research team asserted that Earth’s environment was inhospitable to many forms of life at first, and evolution only became possible when the global environment reached a “permissive state.”
A certain level of oxygen in the atmosphere is required for the existence of complex animal life, so the oxygenation of Earth’s atmosphere through photosynthesizing microbes and bacteria was necessary for the planet to host the development of more recent life forms.
“We’re arguing that intelligent life may not require a series of lucky breaks to exist,” said Dan Mills, the lead author of the study and a researcher at the University of Munich.
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“Humans didn’t evolve ‘early’ or ‘late’ in Earth’s history, but ‘on time,’ when the conditions were in place. Perhaps it’s only a matter of time, and maybe other planets are able to achieve these conditions more rapidly than Earth did, while other planets might take even longer.”
The timing of human origins could have been driven by changes in sea surface temperature, ocean salinity levels, availability of nutrients, and the amount of oxygen in the atmosphere.
The researchers believe that predictions about the evolution of life should be based on a geological time scale rather than the lifespan of the sun.
They plan to test their model against the proposed “hard steps” theory and search the atmospheres of planets outside our solar system for biosignatures.
The study was published in Science Advances.
