co₂-metabolism hypothesis

proto-metabolic threshold behavior in alkaline hydrothermal vent chemistry

P(HL) vs N — probability of a Lane-like proto-core

N* at λ=0.1
P(HL) ≥ 0.5
N* at λ=0.15
72
P(HL) ≥ 0.5
N* at λ=0.2
54
P(HL) ≥ 0.5
N* at λ=0.25
42
P(HL) ≥ 0.5

Nick Lane's hypothesis proposes that life originated not from a prebiotic soup but from the geochemistry of alkaline hydrothermal vents. Where hydrogen-rich fluids from serpentinizing rock met CO₂-laden ocean water, a natural electrochemical gradient drove carbon fixation — the same reaction that powers the acetyl-CoA pathway in modern methanogens and acetogens.

The 4-reaction Lane motif — a minimal proto-metabolic core:

r1: CO2+H2MA\text{r1: } \text{CO}_2 + \text{H}_2 \xrightarrow{M^*} A
r2: AMC\text{r2: } A \xrightarrow{M^*} C
r3: ACB\text{r3: } A \xrightarrow{C} B
r4: A+H2C2A\text{r4: } A + \text{H}_2 \xrightarrow{C} 2A

A = activated intermediate, C = catalyst/cofactor, B = boundary precursor. Reaction r4 is autocatalytic: the system can amplify itself.

This playground models a threshold question: molecules are randomly assigned roles (A, C, B) and distributed across vent pore compartments. Each compartment is checked for a Lane-like motif. The central parameter is catalytic density λ — the probability that any given molecular interaction actually catalyzes a reaction.

The expected motif count scales as:

μpApCpBN3λ4q2\mu \approx p_A \cdot p_C \cdot p_B \cdot \frac{N^3 \cdot \lambda^4}{q^2}

As N grows, proto-cores become probabilistically inevitable — not guaranteed in any single compartment, but increasingly hard to avoid across the ensemble.

The threshold N* marks where P(HL) crosses the target probability. Empirically, N* scales with λ as a power law. The heuristic analysis predicts:

Nλ4/3N^* \propto \lambda^{-4/3}

Higher catalytic density dramatically lowers the molecular threshold for proto-metabolic emergence.

Compartmentalization matters: vent pores act as natural reaction vessels. More pores (higher q) dilute molecules across compartments, pushing thresholds upward. But each pore provides an independent trial — a tradeoff between concentration and combinatorial opportunity.

This is a toy model — no stoichiometry, kinetics, or thermodynamics. It captures threshold behavior, not chemistry. The point is that the transition from "possible" to "nearly forced" can be sharp, and that sharpness does not depend on any one lucky compartment but on the statistics of the entire vent system.