24 January 2016

Gaian bottleneck means alien life never persists, say Oz astrobiologists

by Will Parker

Life on other planets would likely be brief and become extinct very quickly, according to a new paper by astrobiologists at the Australian National University. In research aiming to understand how life might develop, the scientists realised new life would commonly die out due to runaway heating or cooling on their fledgling planets.

"The universe is probably filled with habitable planets, so many scientists think it should be teeming with aliens," said Dr Aditya Chopra, lead author of the paper, which was published in Astrobiology.

"Early life is fragile, so we believe it rarely evolves quickly enough to survive," Chopra explained. "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 paper suggests that 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.

"Early microbial life on Venus and Mars, if there was any, failed to stabilise the rapidly changing environment," said paper co-author Charley Lineweaver. "Life on Earth probably played a leading role in stabilising the planet's climate."

Chopra added that their theory solved a longstanding puzzle. "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," 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 plausible solution to Fermi's paradox, say the 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 Lineweaver.

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Source: Australian National University