If extraterrestrials do exist, they sure have a good way of hiding themselves. Perhaps, it’s their absurdly advanced stealth technology that’s to blame for our searches for life outside Earth returning fruitless.

But if life evolves on a trajectory towards intelligent and technological civilizations, then where is everybody?

Astrobiologists from Australian National Univ. have posited that potential extraterrestrials are silent because they’re already dead, and most likely went extinct during a very primitive state of life.

Their research was published in Astrobiology.     

“The universe is probably filled with habitable planets, so many scientists think it should be teeming with aliens,” said paper author Aditya Chopra, of the university’s Research School of Earth Sciences. “Early life is fragile, so we believe it rarely evolves quickly enough to survive. Most planetary environments are unstable. To produce a habitable planet, life forms need to regulate greenhouse gases such as water and carbon dioxide to keep surface temperatures stable.”

According to the researchers, Venus, Earth, and Mars likely started off with similar conditions 4 billion years ago. The planets were hot from accretion, and wet from aqueous bodies impacting beyond the snowline. But eventually, Venus lost the majority of its water while Mars lost around 85% and the rest was frozen. 

“If life emerges on a planet, it only rarely evolves quickly enough to regulate greenhouse gases and albedo, thereby maintaining surface temperatures compatible with liquid water and habitability,” the researchers write. In the proposed model, “the maintenance of planetary habitability is a property more associated with an unusually rapid evolution of biological regulation of surface volatiles than with the luminosity and distance to the host star.”

The new model, the researchers said, presents a possible solution to Fermi’s paradox. They’ve titled this model of near universal extinction the Gaian Bottleneck

Paper co-author Charles H. Lineweaver said, “One intriguing prediction of the Gaian Bottleneck model is that the vast majority of fossils in the universe will be form extinct microbial life, not from multicellular species such as dinosaurs or humanoids that take billions of years to evolve.”