Do you ever gaze into the yawning expanse of stars and question what else is out there? Do you ever wonder if far-flung alien species are contemplating the same thing?
You can stop dreaming, star child, because all those diverse forms of life probably died in the evolutionary womb. According to a new Australian National University paper published in Astrobiology, the spark of life is rare and, when it occurs, most likely perishes in early extinction.
The authors, Dr. Aditya Chopra and Dr. Charles H. Lineweaver call their model the "Gaian bottleneck" and present it as a solution to Fermi's paradox, which in turn outlines the contradiction between the probability of alien life and the stunning silence we've experienced thus far from the intergalactic community.
Simply put, where is everybody? Why does extraterrestrial life seem to exist solely in fantasy? Various bottleneck theories attempt to answer this question, accounting for key challenging moments in the ascension of any given planetary ecosystem.
If life on, say, Shnuborg 7 was snuffed at the chemical level, then you've got an emergence bottleneck on your hands. On the far end of the civilization timeline, perhaps the Shnuborgians destroyed themselves in a nuclear war over resources — a classic self-destruction bottleneck.
But if the emergence bottleneck reduces the likelihood of extraterrestrial life, that means Earth has already survived the greatest risk to its continued survival. Meanwhile, if the self-destruction bottleneck is the deciding factor, then earthlings still have a tough road ahead of them between now and global world peace.
The Gaian bottleneck presents an alternative option less poisoned by nihilism or earthling exceptionalism. Chopra and Lineweaver postulate that life's core challenge comes in the form "strong selection pressure to actively modify and regulate its environment."
In other words, for life to evolve beyond microbial level, it has to transform a primordial, unstable environment into a habitable planet. That means, among other parameters, regulated greenhouse gases and stable surface temperatures.
If true, the Gaian bottleneck theory means that the success of life on Earth depended less on specific chemical ingredients or decreased cosmic bombardment rates. Instead, we can thank our planet's rapid biological evolution during its first billion years — an evolution that effectively terraformed the world.
How will this theory pan out? We'll have to see what else we find — and what finds us — out there in the cosmos. However, the authors do point out that a discovery of extant independent life on Mars would be a major blow to their theory, while the discovery of extinct independent Martian life would be right in line with the Gaian bottleneck model.