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An Astronomer Considers the Origin of Life, with Sobering Results

Rob Sheldon

origin of life

Live Science reports:

Is life a gamble? Scientist models universe to find out

Scientists suspect that the complex life that slithers and crawls through every nook and cranny on Earth emerged from a random shuffling of non-living matter that ultimately spit out the building blocks of life.

Even so, the details to support the idea are lacking.

But researchers recently got creative in figuring out the probability of life actually emerging spontaneously from such inorganic matter — a process called abiogenesis.

In the study, Tomonori Totani, a professor of astrophysics at the University of Tokyo, modeled the microscopic world of molecules across the epic scale of the entire universe to see if abiogenesis is a likely candidate for the origin of life. He was essentially looking at whether there were enough stars with habitable planets in the universe at the time to allow complexity to arise. His results, published Feb. 3 in the journal Nature, show the betting odds for life emerging are not good, at least for the observable universe.

A Cross-Over Attempt

The article is sobering, because biologists are generally bad with big numbers, and astronomers love big numbers but are bad with cellular biology. This is a cross-over attempt by a Japanese astronomer to do RNA-world origin-of-life calculations. His paper can be found here. 

He decides that the RNA-world “origin-of-life” game can be won if he can accidentally make a self-replicating RNA strand. As per the rules of the game, assume an ocean full of RNA monomers (nucleotides) just waiting to be hitched up. Yes, this is like saying “assume the answer minus the last step.” And no, it is even more unlikely than the last step, but those are the rules.

He’s pseudo-realistic enough to know that it takes 40-100 nucleotides to make a catalytic RNA strand. Given that there are 4 possible nucleotides for each position, that is 4^(40) up to 4^(100), or 1.2×10^(24) up to 1.6×10^60 permutations for that magic sequence. But the probability is worse than this, because (a) we need two strands to replicate — one to be the template, the other to be the enzyme, and (b) when this experiment is done in the lab, we never get more than about 10 nucleotides long, because the shorter ones outnumber the longer ones. This is precisely what you would expect from “diffusion-limited growth,” where big snowflakes grow more slowly than small ones, so all the snowflakes come out the same size.

(a) means that you have to have twin RNA molecules meet each other in the ocean. Making the ocean bigger to get the first one makes it harder for the second one to meet it. You just can’t win this game by dumping the entire jar of Fischer Scientific reagents into the Erlenmeyer flask. (They tried.)

(b) means that it isn’t just the number of permutations that slow down the synthesis, it’s the competition with all the shorter RNA strands. For diffusion-limited growth, you can think of it as the “active” end of the RNA becomes a decreasing percentage of the surface of the RNA. Once the RNA coils or bunches or clumps, the active ends aren’t even available to add more nucleotides. So you have a probability that goes as P = 1/N! * exp^(-kN).

Ignoring Biology and Chemistry

Alas, already the esteemed astronomer has ignored the physics. He assumes that monomers add by a Poisson process, which means the rate of polymerization is independent of length. It makes for pretty math and drops a few thousand orders of magnitude from the probability, but it totally ignores both the biology and the chemistry. For the record, that’s the second tooth fairy.

Just to make things worse, he assumes clay will catalyze the reaction, seemingly unaware that clay is a bio-mineral that doesn’t form on its own. But out of mercy, we’ll let that tooth fairy pass.

Then he adds an “evolution” probability to his calculation. I assume that this is the probability that the twin monomers will not only produce offspring, but twin mutated offspring. Now evolution is one of the requirements for living things, and he wants living things to be created by evolution! There are numerous quotes by the great minds of Darwinism saying that abiotic chemistry does not possess evolution. It really feels like this step is buying the farm. So this seems to be a third tooth fairy.

A Quasi-Drake Equation

He ends up with a quasi-Drake equation of five unknown probabilities for the probability of OOL. One of them is the number of nucleotides in his ocean. He plugs in a number like 10^(25) by assuming they are delivered by carbonaceous chondrite meteorites. Now since these same CI meteorites have fossilized cyanobacteria on them, the whole calculation should be finished — life spontaneously appears. But instead, he assumes the fossils don’t exist, but the nucleotides do, being made in the Great Cosmic Abiotic Nucleotide Factory in Outer Space. Just for the record, that GCANFOS also makes only chiral amino acids and chiral nucleotides using the same deep magic. I’m going to give that a fourth tooth fairy.

He goes back to the lover’s paradox of twins finding each other in the vast ocean, and decides that it is equivalent to making an RNA strand twice as long. I didn’t follow the logic, but then he’s not paying any attention to the chemistry either. So he raises his minimum RNA length from 80-200 bases long. That’s now 10^48 — 10^120 permutations, but at least it no longer penalizes the quasi-Drake equation for adding more volume, or penalizes the diffusion-limited growth length. Once again, I find this a somewhat dishonorable way to solve the lover’s paradox, but I’ll let this one be a part of tooth fairy number two.

After grinding through this calculation with these most favorable of odds for the final step of RNA-world, he still is short some 78 orders of magnitude. Putting that into perspective, the visible universe has 10^80 equivalent H-atoms, so this is like finding a single silver atom in the entire universe. This causes him to write the only reasonable sentence in the whole paper:

If we consider only the conservative abiotic polymerization, i.e., statistically adding monomers, the probability of abiogenesis may be extremely low on a terrestrial planet.

Which he follows with what is perhaps the least reasonable sentence in the paper:

This case is not in contradiction with our existence on Earth, because we would find ourselves on a planet where abiogenesis happened.

One Tooth Fairy Per Theory

In other words, since we are here, evolution is true and so is OOL. How’s that for crushing logic?

In my opinion, only one tooth fairy is allowed per theory, and this one has at least four, making its irrelevance nearly guaranteed. But what he does next, gives away the entire game:

The observable universe is just a tiny part, whose volume is likely smaller than 1/10^(78) of the whole universe created by an inflation, and there is no strong reason to expect more than one abiogenesis event in such a small region.

He says, in effect, we can just add 78 orders of magnitude to our calculation by invoking an inflationary universe, so the real universe has whatever probabilistic resources needed, since inflation could add 36 orders of magnitude, 150 orders of magnitude, or even 1,000 orders of magnitude, being entirely unconstrained by observations and therefore entirely metaphysical. Being metaphysical, we can call inflation whatever we want, so let’s just call it “god” consistent with what it is called in most of the historically important literature.

Why do I find this sobering? Because it shows that OOL is not progressing, but regressing — adding bad physics to already bad chemistry and bad biology — even after restricting itself to the most trivial of steps.

Image: Kepler-1649c (artist’s imagining), an “Earth-size exoplanet orbiting in its star’s habitable zone,” by NASA/Ames Research Center/Daniel Rutte.