Plate tectonics, oceans and continents may be the secret ingredients for complex life on Earth. And if these geological features are rare elsewhere in the universe, that may explain why we haven’t yet discovered intelligent alien life. New research from American and Swiss geoscientists suggests that these ingredients represent missing variables in the famous Drake equation, devised more than half a century ago to estimate the odds of finding advanced civilizations in our galaxy. Including these new variables could completely rewrite the odds of detecting intelligent life in the Milky Way.
The impetus for this research, with its galaxy-wide implications, began with a mystery here at home: Why did it take so long for life to expand beyond simple organisms?
“Life has existed on Earth for about 4 billion years, but complex organisms like animals didn’t appear until about 600 million years ago, which is not long after the modern episode of plate tectonics began,” said Robert Stern of the University of Texas at Dallas. “Plate tectonics really gets the evolutionary machine going, and we think we understand why.”
Stern and his collaborator, Taras Gerya of the Swiss Federal Institute of Technology, argue that plate tectonics – the grinding motion of the planet’s upper layers over long geological timescales – accelerated the transition to complex life.
Early in Earth’s history, simple organisms emerged in the ocean, but humanity—an advanced civilization capable of communicating across space—could not exist if ancient life had not moved to the land. Large, resource-rich continents were therefore an essential prerequisite for what Stern and Gerya call Active Communicative Civilizations (ACCs), such as humanity. But that alone was not enough: the continents had to move.
Geological evidence on Earth shows that plate tectonics accelerated evolution on land through five distinct processes: it increased the supply of nutrients, accelerated the oxygenation of both the atmosphere and the ocean, moderated the climate, caused a high turnover of habitat formation and destruction, and provided noncatastrophic pressures on the environment that forced organisms to adapt.
The end result of all this pressure on the environment: us.
If Stern and Gerya are correct, plate tectonics was a prerequisite for later innovations such as the wheel, the smartphone, and the Apollo program.
And for other civilizations in the Milky Way to develop similar technological marvels, their planets may also need plate tectonics. But as far as we know, these are rare.
Earth is the only planet in our solar system with plate tectonics. Volcanism exists on some other worlds, such as Venus, Mars, and Io, but these worlds have a single solid shell rather than multiple moving plates. Similarly, ocean worlds such as Enceladus and Europa are bound within an icy shell, preventing any hypothetical life there from transitioning to land.
We don’t know for sure whether distant solar systems contain planets with plate tectonics – current space telescopes don’t have the resolution to make such determinations. But knowing that they might not makes a more precise version of the Drake equation possible.
Two key factors are proposed in the revised equation: the percentage of habitable exoplanets with large continents and oceans, and the percentage of exoplanets with plate tectonics lasting longer than 500 million years.
This version is much more nuanced than the original Drake equation, which only took into account the number of habitable planets on which intelligent life had evolved.
“In the original formulation, it was thought that this factor was close to 1, or 100 percent — that is, evolution on all planets with life would proceed and, given enough time, turn into an intelligent civilization,” Stern said. “Our perspective is: That’s not true.”
Indeed. Their math reduces the percentage of these planets developing ACCs to just 0.003% at the minimum and 0.2% at the maximum – a far cry from the original 100%.
When you combine these factors of the Drake equation with the number of stars formed each year, the number of stars with planets, the number of habitable planets, the number of habitable planets with life, the number of civilizations on those planets emitting detectable signals, and how long they emit those signals, the chances of finding intelligent extraterrestrial life become significantly smaller.
The implications of the original Drake equation were that ACCs should be common and that we should see them everywhere. But including plate tectonics in the equation changes the result and makes it perfectly understandable why we don’t see ET everywhere in the galaxy.
So intelligent alien life may be rarer than anyone thought. And Earth may be more special than we knew. And it’s all thanks to our planet’s fragmented, unruly, shifting topsoil.
Find out more:
Amanda Siegfried, “Geoscientists Investigate Why We May Be Alone in the Milky Way.” University of Texas at Dallas.
Robert Stern and Taras Gerya, “The importance of continents, oceans, and plate tectonics for the evolution of complex life: implications for finding extraterrestrial civilizations.” Scientific reports.