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It has been presumed that in order for life to develop on a planet, it would need to have plate tectonics, but a new paper suggests otherwise.
In our efforts to find evidence for alien life in the vastness of the universe, scientists determined that the best way to narrow the search down was to determine a key set of necessary ingredients.
Among them, of course, is liquid water on the surface, or biosignatures of CO2 in a planet’s atmosphere. Another one considered equally important was the existence of plate tectonics.
This is because volcanoes exist around the border of these plates and release gases into the atmosphere.
Through weathering, the released CO2 is pulled down to the surface where it seeps into the surface rocks and sediment, possibly creating life.
The process of subduction – where one plate is pushed deeper by another – is also known to aid carbon cycling by pushing carbon into the mantle.
One giant floating plate
But now, in a paper published to Astrobiology, a team from Penn State University has stated that plate tectonics might not be as necessary as we once thought.
On a planet without plate tectonics – known as a stagnant lid planet – the crust is just one giant, spherical plate floating on a mantle. These are believed to be much more widespread then planets with different plates.
After creating a computer model of a stagnant lid planet’s life cycle, the team estimated how much heat it could retain. After running hundreds of simulations, it found that these planets can sustain conditions for liquid water for billions of years. At the highest extreme, they could sustain life for up to 4bn years, roughly Earth’s life span to date.
Finding the sweet spot
“You still have volcanism on stagnant lid planets, but it’s much shorter-lived than on planets with plate tectonics because there isn’t as much cycling,” said Andrew Smye of the research team.
“Volcanoes result in a succession of lava flows, which are buried like layers of a cake over time. Rocks and sediment heat up more the deeper they are buried.”
The simulations also showed that at high enough heat and pressure, CO2 can escape from rocks and make its way to the surface, similar to what happens in subduction fault zones.
This process would increase based on what types and quantities of heat-producing elements are present in a planet up to a certain point.
Bradford Foley, also of the team, added: “There’s a sweet-spot range where a planet is releasing enough CO2 to keep the planet from freezing over, but not so much that the weathering can’t pull CO2 out of the atmosphere and keep the climate temperate.”
