We Can’t Find Aliens Because They’re All Extinct

Alien life may well have flourished many times around our galaxy, and even our solar system. Why haven’t we found it, though? It probably lived and died long before we were around, and didn’t last long enough to evolve into complex multicellular forms. A new study published by scientists and researchers at the Australian National University suggests that near-universal early extinction of other lifeforms in our universe — at a cellular and microbial level — is due to the relatively rapid change of the climates on planets like Venus and Mars.

Astrobiologists Aditya Chopra and Charles H. Lineweaver, from the Planetary Science Institute and the Research School of Astronomy and Astrophysics at ANU, have released a paper saying that the lack of life on other planets — despite the ingredients for life being abundantly available — may be due to a complex interaction between the planets themselves and the life that evolves on them.

In Chopra and Lineweaver’s model, which they call the Gaian bottleneck, the emergence of life on a planet is tied to its ability to evolve rapidly enough to regulate its greenhouse gas emissions, which in turn affect the albedo of the planet through the amount of frozen and liquid water and other reflective materials, which in turn affects the surface temperature.

In extremely rare cases — like on Earth — the relatively rapid evolution from single- to multicellular organisms to complex life forms did not produce enough greenhouses gases to cause runaway negative feedback and heat the planet enough to evaporate all its liquid water. It’s that particular and so far unique quirk that has kept us alive, if the Gaian bottleneck explanation is accurate.

The Fermi paradox is the apparent discordance that exists between that possibility of successful multicellular life on rocky planets around the universe other than our own, and the complete lack of evidence that any life other than on Earth has existed for more than a cosmic microsecond. The traditional explanation for this is an emergence bottleneck explained by the Great Filter, but the Gaian bottleneck is an alternative that seems, at face value, to be equally likely. [Australian National University]

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