I just posted something in a Reddit comment that I thought I should also share here:

There's a very real possibility that the Fermi Paradox actually arises because it doesn't take into account that rocky planets didn't exist for most of the universe's history!

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Recent observations are making it clear that planet formation around a star depend very, very heavily on the metallicity of the star(s) that formed the parent nebula. If you don't have abundant "metals", meaning elements heavier than helium, then rocky planets can't form.

Stars have been building up metallicity since the Big Bang, when only hydrogen and helium existed (plus traces of lithium). Stars are powered by converting lighter elements into heavier ones, and the process of enriching elements like silicon and iron is slow.

Our own Sol has a very high concentration of metals, and we now know from exoplanet research that this is probably why Sol-like planetary systems are rare: if a star begins from material with more metals, planet formation around the star looks very different.

That means that Earth is very likely to be part of the first generation of planets *in the universe* where life is possible. Maybe those other planets are teeming with life, but none of it is any older than we are.

My favorite abiogenesis theory is the alkaline vent hypothesis. Olivine rock, which is common in our solar system, reacts with acidic water to weather into serpentine rock, and in the process it becomes porous and releases alkalinity. Those pores are roughly cell-sized...

... and the pH gradient is very reminiscent of the pH gradients that cells use to drive metabolic reactions, such as creating ATP.

Since oceans in a reducing atmosphere are naturally acidic due to dissolved CO2, this suggests that any rocky world with olivine, liquid water, and a CO2 atmosphere should host microbial life. But due to stellar metallicity, Earth is among the first of such worlds.

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