We’re here. We’re not entirely sure how we got herebut we’re here.
But… what if we weren’t here?
That’s the question scientists posed in a new study, simulating an alternative vision of Earth where life, uh, never found a way.
The findings, reported in The Planetary Science Journalaren’t just a surreal thought experiment.
It’s also a serious scientific question, and a new investigation of the ideas behind the Gaia hypothesis.
The Gaia hypothesis – not to be confused with the mythologically similar-sounding Theia hypothesis – proposes that life on Earth interacts with the planet’s physical environment in ways that help maintain a habitable world, producing a kind of planetary homeostasis.
In the new research, led by astrobiologist Samantha Gilbert-Janizek at the University of Washington, scientists wound back the clock to see how Earth might develop over billions of years – devoid of any such hypothetical helping hand.
“An open question regarding Earth’s evolution is whether or not it could be habitable over billion-year timescales without life’s influence on the environment,” the researchers write in their paper.
“Clearly, biology plays an important role in Earth’s surface environment, which motivates our central question: Is life required to maintain the long-term habitability of a rocky planet?”
In their study, Gilbert-Janizek and colleagues developed a sophisticated computer model of an Earth without life, but incorporating everything else in its physical environment – including the planet’s core, mantle, crust, atmosphere, oceans, and incoming solar flux – and calculated how chemicals would cycle between different parts of the planet.
In total, they simulated 19 key planetary properties, such as heat flow, ocean chemistry, and surface temperatures, and tracked how this virtual Earth would evolve over 5 billion years, from around the time Earth formed, up until about 500 million years in the future.
Aside from answering existential questions about the fate of our hypothetical lifeless Earth, the simulations could also help us make sense of the atmospheric and chemical signatures we detect on distant worlds.
“This model can help us see how habitable but non-living planets might mimic living planets,” Gilbert-Janizek says.
“When we interpret observations of an exoplanet’s atmosphere, this tool will help us determine the probability that what we observe indicates life on the surface.”
In terms of the lifeless surface of the simulated abiotic Earth, as it turns out, the absence of life doesn’t seem to make a huge difference to how things pan out over billions of years – with the most striking exception being a lack of atmospheric oxygen, given the absence of photosynthesis.
While atmospheric oxygen might be considered non-negotiable for most complex life, it’s not actually a prerequisite for habitability in the context of astronomy, where it’s usually defined by a planet’s ability to support liquid water on its surface.
On that score, the lifeless Earth exhibited similar levels of water to our own Earth, among other things.
“We demonstrate that an Earth-like planet can maintain habitable surface temperatures over 4.5 Gyr of evolution (and longer) through abiotic processes alone, without requiring biological feedbacks for climate regulation,” the team explains.
“The carbonate–silicate cycle, driven by the interplay between silicate weathering, volcanic outgassing, and ocean chemistry, provides a robust negative feedback that keeps atmospheric CO2 and surface temperature within habitable bounds despite the Sun’s luminosity increasing by approximately 30 percent over 4.5 Gyr.”
The findings don’t disprove the Gaia hypothesis, and the researchers note that they can’t rule out the possibility that life on Earth contributes to processes that enhance climate stability.
The researchers also acknowledge several limitations and simplifications in their model, including assumptions about plate tectonics, atmospheric chemistry, and the processes that regulate Earth’s climate.
But nonetheless, the results of their simulation suggest that life is not a requirement for a rocky planet to stay habitable.
“Our findings suggest that the abiotic Earth could evolve to a similar state (in terms of global geophysics and climate) to present-day Earth without life, but without abundant atmospheric oxygen,” the researchers conclude.
“This work thus contributes to the ongoing debate regarding the Gaia hypothesis by suggesting that life and habitability may be somewhat decoupled.”
The findings are reported in The Planetary Science Journal.
This article was fact-checked by Rebecca Dyer and edited by Rebecca Dyer. While we pride ourselves on our process, we are only human. If you spot a mistake, please let us know.
Source: www.sciencealert.com
