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 haven’t discovered intelligent alien life yet. New research by American and Swiss Earth scientists suggests that these ingredients represent the missing variables in the famous Drake equation, devised 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 detecting intelligent life in the Milky Way.
The impetus for this research, with its galaxy-wide implications, began with a mystery right here at home—why did life take so long to get 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 at Dallas. “Plate tectonics really kickstarts the evolutionary machine, and we think we understand why.”
Stern and his collaborator Taras Gerya of the Swiss Federal Institute of Technology suggest that plate tectonics—the 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 across space—could not have existed if ancient life had not transitioned to land. Vast resource-rich continents were therefore essential for what Stern and Gerya call active communicative civilizations (ACCs) such as humanity to develop. But that 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: it increased the supply of nutrients; accelerated oxygenation of both the atmosphere and the ocean; moderated the climate; caused high rates of habitat alteration and destruction; and offered a non-catastrophic environmental pressure that forced organisms to adapt.
The end result of all these environmental pressures: us.
If Stern and Gerya are correct, plate tectonics was a requirement for eventual innovations like the bicycle, the smartphone, and the Apollo program.
And in order 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 such as Enceladus and Europa are bound by an ice sheet that prevents any hypothetical life there from crossing over to land.
We don’t know for sure whether there are plate tectonic planets in distant solar systems—current space telescopes don’t have the resolution to make such determinations. But knowing that may not allow for a more accurate version of the Drake equation.
Two basic factors are 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 refined than the original Drake equation, which simply took into account the fraction of habitable planets that have developed intelligent life.
“In the original formulation, this factor was considered to be close to 1 or 100% – this means that evolution on all planets will move forward with life and, given enough time, will turn into an intelligent civilization,” said Stern. “Our perspective is: That’s not true.
Indeed. Their math reduces the percentage of these planets that develop ACC to just 0.003% at minimum and 0.2% at most – a long way from the original 100%.
When we put that together with all the other factors in the Drake equation: the number of stars formed per year, the number of those stars with planets, the number of those planets that are habitable, the number of habitable planets with life, the number of civilizations on those planets that emit detectable signals, and how long the signals are sending – well, the chances of finding intelligent extraterrestrial life are greatly reduced.
The implications of the original Drake equation were that ACCs should be common and we should see them everywhere. But including plate tectonics in the equation changes the result and makes it clear that it’s perfectly understandable why we don’t see ETs across the galaxy.
So intelligent alien life may be rarer than anyone thought. And Earth may be more special than we knew. All thanks to our planet’s fractured, unruly and shifting upper crust.
More information:
Amanda Siegfried, “Geoscientists Explore 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 the Search for Extraterrestrial Civilizations. Nature Scientific Reports.