The Answer to Fermi’s Paradox? –“Near Universal Early Extinction of Life in the Cosmos” (Friday’s Most Popular)



“The universe is probably filled with habitable planets, so many scientists think it should be teeming with aliens,” said Aditya Chopra at Australia National University. “Early life is fragile, so we believe it rarely evolves quickly enough to survive. Most early 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. The mystery of why we haven’t yet found signs of aliens may have less to do with the likelihood of the origin of life or intelligence and have more to do with the rarity of the rapid emergence of biological regulation of feedback cycles on planetary surfaces.”

In a cogent answer to physicist Enrico Fermi’s famous paradox –if intelligent life exists in the Milky Way, where are they? Life on other planets would likely be brief and become extinct very quickly, say astrobiologists from The Australian National University (ANU). In research aiming to understand how life might develop, the scientists realized new life would commonly die out due to runaway heating or cooling on their fledgling planets.

But in 1950, Fermi made a seemingly innocuous lunchtime remark that has caught and held the attention of every SETI researcher since. The remark came while Fermi was discussing the possibility that many sophisticated societies populate the Galaxy. They thought it reasonable to assume that we have a lot of cosmic company. But somewhere between one sentence and the next, Fermi’s supple brain realized that if this was true, it implied something profound. If there are really a lot of alien societies, then some of them might have spread out.

Fermi realized that any civilization with a modest amount of rocket technology and an immodest amount of imperial incentive could rapidly colonize the entire Galaxy. Within ten million years, every star system could be brought under the wing of empire. Ten million years may sound long, but in fact it’s quite short compared with the age of the Galaxy, which is roughly ten thousand million years. Colonization of the Milky Way should be a quick exercise.




So what Fermi immediately realized was that the aliens have had more than enough time to populate the Galaxy with their presence. But looking around, he didn’t see any clear indication that they’re out and about. This prompted Fermi to ask what was an obvious question: “where is everybody?”

A plausible solution to Fermi’s paradox, say the ANU researchers, is near universal early extinction, which they have named the Gaian Bottleneck. “One intriguing prediction of the Gaian Bottleneck model is that the vast majority of fossils in the universe will be from extinct microbial life, not from multicellular species such as dinosaurs or humanoids that take billions of years to evolve,” said co-author Associate Professor Charley Lineweaver from the ANU Planetary Science Institute.




About four billion years ago Earth, Venus and Mars may have all been habitable. However, a billion years or so after formation, Venus turned into a hothouse and Mars froze into an icebox. About four billion years ago Earth, Venus and Mars may have all been habitable. However, a billion years or so after formation, Venus turned into a hothouse and Mars froze into an icebox. About 4.5 billion years ago, the young Mars would have had enough water to cover its entire surface in a liquid layer about 140 m deep, but it is more likely that the liquid would have pooled to form an ocean occupying almost half of the planet’s northern hemisphere, and in some regions reaching depths greater than 1,600 meters.

Early microbial life on Venus and Mars, if there was any, failed to stabilize the rapidly changing environment, said Lineweaver.”Life on Earth probably played a leading role in stabilizing the planet’s climate,” he said.

Wet, rocky planets, with the ingredients and energy sources required for life seem to be ubiquitous, however, as physicist Enrico Fermi pointed out in 1950, no signs of surviving extra-terrestrial life have been found.

A copy of the paper can be downloaded at

The Daily Galaxy via Australian National University and the SETI Institute

Image credits: NASA and ESO Alma Observatory

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