Plate tectonics may be a phase in the evolution of planets that has implications for the habitability of exoplanets, according to new research published this month in the journal Physics of the Earth and Planetary Interiors.
Two of the things that make Earth unique in our solar system are that it has plate tectonics – with the surface broken up into a number of tectonic plates that drift around, moving continents and causing earthquakes – and life.
And there is a school of thought that these two are not unrelated.
Complex life on Earth took a long time to evolve; about 3.5 billion years by current estimates. This was possible as the Earth’s surface has been habitable and in the temperature range for liquid water.
This is a remarkable level of stability, especially as the sun has grown 30% brighter over that same interval, meaning that Earth’s atmosphere has evolved, becoming less of a greenhouse than it was 3 billion years ago.
Plate tectonics provides a mechanism for this global thermostat. Most volcanism on the Earth occurs at plate boundaries in response to plate tectonics. And the most important volcanic products by mass – by a large amount – are two greenhouse gases: carbon dioxide and water.
Tectonic plates around the Earth. Rainer Lesniewski/Shutterstock
As they move over the Earth’s surface, some plates get recycled back into the mantle, at places like the Marianas Trench in the Pacific Ocean.
Enormous amounts of water and carbonate (the mineral form of CO2) get recycled back into the interior as they do.
Plate tectonics also form mountains, and one of the major sinks of CO2 over geological time periods is weathering of mountains, where CO2 dissolved in rainwater reacts with silicate minerals, forming new minerals, and drawing down atmospheric CO2 levels.
In concert, these mechanisms act as a thermostat. If the Earth gets too hot, high levels of rainfall and erosion start bringing CO2 levels down. If the Earth gets too cold and freezes over, the erosion mechanism stops.
But volcanism, due to plate tectonics, continues pumping CO2 into the atmosphere, and levels build up, eventually melting the icecaps. It was this mechanism that allowed Earth to recover from a global ice age in the Neoproterozoic, about 600 million years ago.