A new scientific study suggests that the conditions required for the emergence of intelligent life are far rarer than previously believed. Planets lacking plate tectonics, sufficient CO₂, and oxygen would make such civilizations extremely uncommon. This was stated by Manuel Scherf and Helmut Lammer of the Austrian Academy of Sciences at the Europlanet Science Congress and Division for Planetary Science (EPSC-DPS) conference in Helsinki in September 2025.

Criteria for Intelligent Life

For an intelligent civilization to evolve, a planet must meet strict conditions:

  • Sufficient CO₂: enough for photosynthesis and to prevent atmospheric loss, but not so much that it causes toxicity or overheating.
  • Plate tectonics: regulates CO₂ through the carbon–silicate cycle, maintaining balance.
  • Long-lived biosphere: the biosphere must last longer than the time required for intelligent life to evolve. On Earth, this process took 4.5 billion years. According to the researchers, in about 200 million to 1 billion years Earth’s CO₂ will decrease, and photosynthesis will come to a halt. Scherf noted that one day CO₂ levels would become too low for photosynthesis, and for Earth this would happen in that time range.

Atmosphere and Technology

For a technological civilization, an atmosphere dominated by nitrogen and oxygen is essential:

  • Oxygen: at least 18% is needed to support fire, which is required for metallurgy and toolmaking.
  • Without oxygen, technological evolution would be impossible.

The scientists’ models compared biospheres with different atmospheres and evolutionary timelines. They concluded that if an intelligent civilization exists in the Milky Way, the nearest one could be around 33,000 light years away. For contact to be possible, such a civilization would need to endure for at least 280,000 years, allowing its timeline to overlap with ours. The authors emphasized that the probability of coexistence was very small.

Searching for Life: SETI in Action

Despite the pessimistic outlook, Scherf urged that the search should continue through the SETI (Search for Extraterrestrial Intelligence) program. He argued that if nothing is found, this would confirm the rarity of life, but if something is discovered, it would represent the greatest breakthrough in science. Scherf explained that SETI remained the only way to know for certain: a null result would confirm the theory, while a positive result would be revolutionary.

In Short…

The conditions required for intelligent life—plate tectonics, sufficient CO₂, adequate O₂, and a long-lived biosphere—make such civilizations rare. The closest one might be 33,000 light years away, and its existence would demand at least 280,000 years of stability. The study reinforces the importance of SETI, stressing that humanity may not be alone, but proof is essential.