Plate tectonics, oceans and continents may just be the secret ingredients for complex life on Earth. And if these geological features are rare elsewhere in the universe, then perhaps that explains why we have yet to discover intelligent alien life. New research by American and Swiss Earth scientists suggests that these components represent variables missing from the famous Drake equation, created more than half a century ago to estimate the chances of finding advanced civilizations in our galaxy. Including these new variables could completely rewrite the probability of discovering intelligent life in the Milky Way.
The impetus for this research, with its galaxy-spanning implications, began with a mystery right here at home—why did life take so long to move 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, not long after the modern episode of plate tectonics began,” said Robert Stern of the University of Texas in Dallas. “Plate tectonics really starts the evolutionary machine, and we think we understand why.”
Stern and his collaborator, Taras Gerya of the Swiss Federal Institute of Technology, propose that plate tectonics—the grinding movement of the planet’s upper layers over long geological time scales—helped accelerate the transition to complex life.
Early in Earth’s history, simple organisms formed in the ocean, but humanity—an advanced civilization capable of communicating in outer space—could not have existed unless ancient life had passed on land. Vast, resource-rich continents were therefore a vital prerequisite for the development of what Stern and Gerya call Active Communicative Civilizations (ACCs) like humanity. But this alone was not enough: the continents had to move.
The geologic record on Earth suggests that plate tectonics accelerated evolution on Earth through five distinct processes: increased nutrient supply; accelerated the oxygenation of both the atmosphere and the ocean; softened the climate; caused a high turnover rate of habitat formation and destruction; and provided non-catastrophic environmental pressure that forced organisms to adapt.
The end result of all these environmental pressures: we.
If Stern and Gerya are right, plate tectonics was a requirement for eventual innovations like the wheel, the smart phone, and the Apollo program.
And for other civilizations in the galaxy to develop similar technological marvels, perhaps their planets also need plate tectonics. But as far as we know, they are rare.
Earth is the only planet in our solar system that has 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 like Enceladus and Europa are bound within an icy layer, stopping any hypothetical life there from crossing over to land.
We don’t know for sure whether distant solar systems exhibit planets with plate tectonics—current space telescopes don’t have the resolution to make such determinations. But knowing that they may not enable a more accurate version of the Drake equation.
There are two key factors proposed in the revised equation: the fraction of habitable exoplanets with large continents and oceans, and the fraction of those with plate tectonics lasting more than 500 million years.
This version is much more nuanced than the original Drake equation, which simply considered the fraction of habitable planets on which intelligent life had developed.
“In the original formulation, this factor was thought to be nearly 1, or 100% — that is, evolution on all planets with life would go forward and, given enough time, would turn into an intelligent civilization,” Stern said. “Our perspective is: That’s not true.”
Really. Their math reduces the percentage of these planets developing ACC to just 0.003% at minimum and 0.2% at maximum – a far cry from the original 100%.
When put together with all the other factors of the Drake equation: the number of stars formed each year, the number of those stars with planets, the number of those planets that are habitable, the number of those planets that are habitable with life, the number of civilizations on those planets that send detectable signals, and how long they send the signals – well, the chances of finding intelligent alien life decrease significantly.
The implications of the original Drake equation were that ACCs should be common and we should see them everywhere. But bringing plate tectonics into the equation changes the result and makes it clear that it’s completely understandable why we don’t see ET across the galaxy.
So intelligent alien life may be rarer than anyone thought. And Earth may be more special than we knew. All this thanks to our planet’s fragmented, unruly and displaced upper crust.
Learn more:
Amanda Siegfried, “Geoscientists dig into why we might 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.” Nature Scientific Reports.