New Study Indicates Advanced Alien Societies Are Exceptionally Uncommon

The Milky Way is teeming with countless planets that might support life, yet recent findings shared at the EPSC-DPS2025 Joint Meeting suggest that civilizations capable of interstellar communication are exceptionally scarce. Research led by Dr. Manuel Scherf and Professor Helmut Lammer from Austria’s Space Research Institute in Graz highlights critical factors such as plate tectonics and atmospheric carbon dioxide levels as crucial determinants in the rarity of extraterrestrial intelligent life.

How Plate Tectonics Support Habitability

Plate tectonics play a vital role on Earth by cycling carbon and maintaining climate stability over geological timescales. The movement of tectonic plates helps trap carbon dioxide in the planet’s mantle, lowering atmospheric CO2 levels. This process is key to sustaining a climate conducive to life by preventing extreme greenhouse effects and ensuring long-term habitability.

For alien civilizations to prosper, similar tectonic activity would likely be necessary. Without active plate tectonics, excessive atmospheric CO2 could cause runaway greenhouse conditions, rendering a planet uninhabitable. Dr. Scherf emphasizes this importance, stating that this geological mechanism is so critical that “extraterrestrial intelligences—ETIs—in our galaxy are probably pretty rare.”

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An artist’s impression of our Milky Way Galaxy, showing the location of the Sun. Our Solar System is about 27,000 light years from the centre of the galaxy. The nearest technological species could be 33,000 light years away. Image credit: NASA/JPL–Caltech/R. Hurt (SSC–Caltech).

Carbon Dioxide: Essential for Life and Civilization

During a planet’s formative years, carbon dioxide sustains the biosphere by enabling photosynthesis, which is crucial for life’s emergence. Over billions of years, Earth’s atmosphere evolved from roughly 6% CO2 to less than 0.04%, thanks largely to plate tectonics. This gradual decrease created stable conditions allowing complex organisms and eventually advanced civilizations to evolve.

For intelligent life elsewhere to develop similarly, planets must regulate their CO2 levels effectively. Without this balance, sufficient oxygen for advanced technological processes like metalworking may never arise. Scherf explains the significance of this stability by noting that, “For 10 civilizations to exist at the same time as ours, the average lifetime must be above 10 million years,” underscoring the necessity of prolonged environmental stability for technological progression.

The Extended Journey to Technological Societies

Realizing intelligent civilizations requires both proper environmental conditions and immense spans of time. Earth itself required more than 3 billion years to nurture life forms capable of producing technology. Consequently, the odds of multiple civilizations coexisting concurrently in the galaxy remain low. How long each civilization endures directly affects the chances of overlapping timelines. Scherf’s analysis reveals that it’s not only the emergence of intelligent life but also the longevity of civilizations that sharply limits the number of simultaneous technological societies.

The research concludes that societies with advanced technology are extraordinarily uncommon due to the prolonged, complex processes necessary for their development. Even if simple life is widespread, "the numbers of ETIs are pretty low and depend strongly upon the lifetime of a civilization." In essence, the transition from basic life to enduring technological civilizations is an exceptionally rare event.

Continuing the Search for Intelligent Life Beyond Earth

Recognizing the extreme rarity of intelligent extraterrestrial life, researchers Scherf and Lammer assert that only through persistent efforts, such as the Search for Extraterrestrial Intelligence (SETI), can humanity confirm or refute the existence of alien civilizations. Failure to detect signals would reinforce the view that advanced societies are scarce, whereas detection of extraterrestrial signals would mark a historic scientific achievement. As Scherf puts it, “Although ETIs might be rare there is only one way to really find out and that is by searching for it. If these searches find nothing, it makes our theory more likely, and if SETI does find something, then it will be one of the biggest scientific breakthroughs ever achieved as we would know that we are not alone in the universe.”