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, then that might explain why we haven’t yet discovered intelligent alien life.
New research from American and Swiss earth scientists suggests that these ingredients represent missing variables in the famous Drake equation, which was 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, reports universetoday.com.
The impetus for this research, with its galaxy-spanning implications, started 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 four billion years, but complex organisms such as animals did not appear until about 600 million years ago, which is not long after the modern episode of plate tectonics began,” says Robert Stern of the University of California. Texas in 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 abrasive movement of the planet’s upper layers over long geological timescales – 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 through space — could not have existed if ancient life had not migrated to land. Vast, resource-rich continents were therefore an essential prerequisite for the development of what Stern and Gerya call Active Communicative Civilizations (ACCs) such as humanity. But that alone was not enough: the continents had to move.
The geological record on Earth suggests that plate tectonics accelerated evolution on land through five different processes: it increased the supply of nutrients; accelerated the oxygenation of both the atmosphere and the ocean; the climate tempered; caused a high turnover rate of habitat formation and destruction; and provided non-catastrophic environmental pressures that forced organisms to adapt.
The end result of all this pressure on the environment: us.
If Stern and Gerya are right, plate tectonics was a prerequisite for eventual innovations such as the wheel, the smartphone and the Apollo program.
And if other civilizations in the Milky Way want to develop similar technological wonders, their planets might need plate tectonics too. But as far as we know they are rare.
Earth is the only planet in our solar system with plate tectonics. Volcanism occurs on some other worlds, such as Venus, Mars and Io, but these worlds have a single solid shell, rather than multiple moving plates. Likewise, ocean worlds like Enceladus and Europa are bound by an icy layer, preventing any hypothetical life there from crossing over 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 may not allow for a more accurate version of the Drake equation.
Two essential factors are proposed in the revised equation: the proportion of habitable exoplanets with large continents and oceans, and the proportion of exoplanets with plate tectonics lasting more than 500 million years.
This version is much more nuanced than the original Drake equation, which simply took into account the proportion of habitable planets on which intelligent life had evolved.
“In the original formulation, this factor was thought to be close to 1, or 100% – that is, evolution would march forward on all planets with life and, given enough time, transform into an intelligent civilization,” Stern said . “Our perspective is: that is not true.”
Indeed. Their calculations reduce the percentage of these planets developing ACCs to just 0.003% at minimum and 0.2% at maximum – a far cry from the original 100%.
Along with all the other factors of the Drake equation: number of stars formed annually, number of stars with planets, number of planets that are habitable, number of those habitable planets with life, number of civilizations on those planets that emit detectable signals, and for how long they send out the signals – well, the chances of finding intelligent alien life shrink considerably.
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 outcome and makes it clear that it’s completely understandable why we don’t see aliens all over the galaxy.
So intelligent alien life could be rarer than everyone thought. And Earth may be more special than we knew. All thanks to the fragmented, unruly and changing top layer of our planet.
