The scarcity of oceans, continents, and long-term plate tectonics on exoplanets likely explain the rarity of advanced extraterrestrial civilizations, challenging predictions provided by the Drake equation and addressing the Fermi paradox, researchers suggest.

A new study by University of Texas-Dallas geologist Dr. Robert Stern and colleagues offers a geological explanation for why there is no convincing evidence of advanced extraterrestrial (ET) civilizations, even though the Drake equation predicts that such civilizations should be abundant in our galaxy.

In a study recently published in the journal 12 Scientific Reports.

The researchers concluded that the likely lack of these three requirements in exoplanets would greatly reduce the expected number of such ET civilizations in the galaxy.

“Life has existed on Earth for about 4 billion years, but complex organisms like animals didn’t emerge until about 600 million years ago, shortly after the modern era of plate tectonics began,” said Stern, professor of sustainability and Earth System Sciences in the School of Natural Sciences and Mathematics. “Plate tectonics really drives the evolutionary machinery, and we think we understand why.”

where is everybody

In 1961, astronomer Dr. Frank Drake developed an equation that multiplied several factors to estimate the number of intelligent civilizations in our galaxy that had the ability to make their presence known to humans:

N = R* X F _P X N _to X F _I X F _I X F _C X L

N: The number of civilizations in the Milky Way galaxy whose electromagnetic radiation (radio waves, etc.) can be detected.

R*: The number of stars formed annually.

F_P: Fraction of stars with planetary systems.

N_to: Number of planets with habitable environments in the solar system.

F_I : The fraction of relevant planets where life actually occurs.

F_I : The fraction of inhabited planets on which intelligent life has arisen.

F_C : The faction of civilizations that have developed technology that creates visible signs of their existence.

L: Average time (years) it took for these civilizations to produce these features.

Assigning values ​​to the seven variables was a clever guessing game that led to the prediction that such civilizations must be common. But if that’s true, why is there no convincing evidence for their existence?

This contradiction is known as the Fermi Paradox and is named after nuclear physicist and Nobel laureate Dr. Enrico Fermi, who informally posed this question to his colleagues.

In their study, Stern and Geria propose refining one of the factors of the Drake equation – f. _I the fraction of habitable planets on which intelligent life has arisen; to explain the need for large oceans and continents, and the existence of plate tectonics on these planets for more than 500 million years.

“The original formulation was that the ratio was close to 1, or 100%, meaning that all life-supporting planets would evolve and, given enough time, become an intelligent civilization,” Stern said. “Our view is: That’s not true.”

The influence of plate tectonics

Plate tectonics is a theory formulated in the late 1960s that states that the Earth’s crust and upper mantle are divided into moving segments, or plates, that move very slowly—about as fast as fingernails and hair grow.

Earth, the only one of four rocky bodies in our solar system with surface deformation and volcanic activity, has plate tectonics. The other three (Venus, Mars and Jupiter’s moon Io) are actively deforming and have young volcanoes, but do not have plate tectonics, Stern said. The other two rocky bodies (Mercury and the Moon) have no such activity and are tectonically dead.

“It’s much more common for planets to have a solid outer shell that doesn’t break apart, known as single-cap tectonics,” Stern said. “But plate tectonics is much more effective at enabling advanced life forms to emerge than single-cap tectonics.”

As tectonic plates move, they collide or push against each other, creating geological structures such as mountains, volcanoes, and oceans, which also contribute to moderate weather and climate. Nutrients enter the oceans due to weathering. Plate tectonics create and destroy habitats, creating moderate but constant stress on the environment for species to evolve and adapt.

Stern and Geria also appreciated the importance of the continued existence of large land masses and oceans for the evolution that led to the emergence of active species capable of communication.

“The ACC requires both continents and oceans because the evolution from simple to complex multicellular life must have occurred in water, but further evolution would lead to ideas about the night sky, the use of fire, the use of metals to create new technologies, and finally the emergence of the ACC. Projects capable of transmitting radio waves and sending rockets into space would have to occur on land, Stern said.

Refinement of the Drake equation

The research team suggested revising the Drake equation that defines f._I as the product of two terms: f_revengefractions of inhabited exoplanets with significant continents and oceans, and f_pointparts of the planets with long plate tectonics.

Based on their analysis, Stern said the fraction of exoplanets with optimal water volume is likely very small. They estimate the value of F_revenge in the range of 0.0002 to 0.01. Similarly, the team concluded that plate tectonics that have persisted for more than 500 million years are also highly unusual, leading to an estimate of f._point Less than 0.17.

“When we multiply these factors together, we get a precise estimate of f._I“This is a very small value, between 0.003 percent and 0.2 percent, rather than 100 percent,” Stern said. “This explains why planetary conditions favorable for the development of intelligent life are extremely rare in our galaxy and resolves the Fermi Paradox.”

According to NASA, more than 5,000 exoplanets have been confirmed in the Milky Way through ground-based observations and orbital platforms such as the Kepler and James Webb space telescopes. While scientists, including University of Dallas planetary researcher and associate professor of physics Dr. Kaloyan Penev, have improved their search for planets around other stars and estimates of the number of rocky planets, they are yet to detect plate tectonics on exoplanets.

“Biogeochemistry suggests that a solid Earth, particularly plate tectonics, accelerated the evolution of species,” Stern said. “Studies like ours are useful because they encourage broad thinking about larger mysteries and provide an example of how we can apply our knowledge of Earth’s systems to interesting questions about our universe.”