In my continuing pursuit of Fermi’s Paradox, we have yet another theory: The Gaia Hypothesis.
As simply as I can… The early formation and saturation of microbial life on Earth allowed for the stabilization of the conditions that supported life. Life begat life. Without life assisting in the stabilization of the carbon cycle, the atmospheric conditions would have swung to extremes. Extremes which, like Mars and Venus, too cold or too hot, would have extinguished life.
If microbial life doesn’t form quickly enough, stick around long enough, and permeate the ecosphere then any planet (in the Goldilocks zone) will drift into uninhabitable conditions. Biological life has had 3.8 billion years to transform the planet’s surface. And it has. Without early life, the theory goes, Earth would have succumbed to runaway greenhouse conditions like Venus, boiling off its water, rendering it inhospitable. Or, would have froze up—permanently, like Mars.
Now, I have trouble with this theory as it ignores the impact of the other features that, among many others, are unique to Earth, namely, a massive Moon, active tectonic plates and just enough radiation to retain the perfect balance of volcanism and carbon weathering and biotic sequestration. But, it cannot be denied that early life DID have an impact and DID assist in the creation of conditions ripe for multicellular life’s burgeoning explosion in the last 600 million years or so.
(Besides, if it weren’t for the Carboniferous period and the surrounding ±50 millions years, the gigatons of carbon (coal and crude oil) would never have been deposited and made available to humans for exploitation. This is yet another future series topic that we’ll explore regarding Fermi’s Paradox.)
The Gaian Bottleneck, as it’s called, undoubtedly had an impact. Is it the sole reason for the dearth of aliens we expect to see in the night sky? No. But it can be added to the coin-flip probability equation we’ve been building. 2^70 Unique.