Terrestrial Abiogenesis

The question of abiogenesis links to the Fermi Paradox: "If the Universe is so big, why are we the only ones here?". Out of all of the potential great filters ("technological civilizations are doomed to collapse", "intelligent life is rare", "multicellular life is rare") the first filter is that maybe life itself is very rare.

This is the first moment of pushback: If life is so rare, what are the odds that it would happen on Earth?

This is a variation of the Mediocrity Principle (and, relatedly, the Copernican Principle). The Mediocrity Principle is so ingrained that many people (whom I've had the pleasure to discuss the Fermi Paradox with) assume that life must have started elsewhere first. To them, it's "more likely" that life started somewhere else, and then the mechanism of panspermia brought it to Earth (by having the simpler lifeforms hitch a ride on a comet, say). This position is rational, but it doesn't get us closer to answering so, where did life come from?

For me, the Anthropic Principle is a good answer to the "modest" presumptions of the Mediocrity Principle. We can observe our own existence, which means there is something already special about us. If life is possible at all, then, if it didn't start on Earth, it would've happened somewhere else, and the same observational bias would apply there too.

What's exciting about this moment is that we may find out in the next quarter century if life is elsewhere in our solar system. If we find life beneath Enceladus then we may get closer to answering the question of rarity. If we find DNA-based life, then it's a strong case that panspermia between Enceladus and Earth happened. (But, in which direction?) If we find life that has no connection to Earth's, then that could suggest life forming around hydrothermal vent-like situations is common.

I'd wager we won't find life on Mars or Enceladus—and, if we were to, it would have been from a terrestrial origin. The Dark Forest Hypothesis makes for interesting science-fiction, but it's a much more complex and circumstance-dependent framework than what the evidence so far suggests: Life simply is that rare.

One resolution to the Fermi Paradox is the Rare Earth Hypothesis: all of the small, unique qualities that make Earth different from other points in the Universe allowed for life to thrive and evolve. I think it's through this same lens that we should consider abiogenesis.

By thinking about terrestrial abiogenesis in particular, we aren't kicking the can down the road, leaving the origins of life to have taken place somewhere else, in conditions unknown. If we limit our search to the conditions of primordial Earth, we have a chance to discover what the possible pre-evolutionary mechanisms were that allowed for life to bootstrap itself into existence.

In Sara Imari Walker's excellent book Life as No One Knows It she asks us to consider definitions of "life" from an information perspective. Walker argues that complex life could not have happened just "randomly." Sure, if you have a primordial soup with Brownian motion you can observe more complex molecules being made, but that will soon lead to a non-reactive pool of tar. Randomness alone does not explain how the information required to allow for the replication of ever more complex molecules could come about.

Instead of starting from the most simple conditions (a hydrothermal vent, a primordial pool) I think we should invert the search: Given all of the conditions we know applied to primordial earth, each condition should be assumed to be essential until we can rule it out.

Breaking it down, this means we need to consider:

• The Earth's surface: it has oceans and dry land. The interface between them should be entertained as essential.

• The Moon: tidal pools create another interface, and a cyclic pattern.

• The Late Heavy Bombardment: that life only started after the LHB should make us ask: what did it bring that was essential to life? (This allows for weak panspermia; the idea that life didn't have a non-terrestrial origin, but it needed exotic elements from elsewhere to help kickstart it.)

• Hydrothermal Vents: I suggested that hydrothermal vents do not appear to be a convincing origin point for life, but that does not rule them out from serving a vital role.

• The Day/Night Cycle; The Wet/Dry Cycle; The Wind -- all of these phenomenons create more opportunities for motion and energy dissipation.

• Volcanic Glass (from Earth, Mars, or even Venus)

Putting this all together, we may consider a tidal pool that is being fed a stream of molecules from a hydrothermal vent, where a lens of volcanic glass modulates the UV spectrum for pre-biotic molecules to conditionally react. Each mechanism may be essential, and until we build more sophisticated models, all of them, and their interfaces, are worthy of study.