On the Rate of Abiogenesis from a Bayesian Informatics Perspective

TL;DR

This paper evaluates how different types of evidence influence our understanding of the spontaneous origin rate of life, emphasizing the complementarity of observational, experimental, and survey data in Bayesian inference.

Contribution

It introduces a framework to compare the informational impact of various experiments on the abiogenesis rate using Bayesian and entropic measures.

Findings

Experiments 1 and 2 only provide lower bounds on the rate.

Evidence for earlier life start has limited impact if the rate is very high.

Exoplanet biosignature surveys are the most direct method to measure the rate.

Abstract

Life appears to have emerged relatively quickly on the Earth, a fact sometimes used to justify a high rate of spontaneous abiogenesis ($\lambda$) among Earth-like worlds. Conditioned upon a single datum - the time of earliest evidence for life ($t_{\mathrm{obs}}$) - previous Bayesian formalisms for the posterior distribution of $\lambda$ have demonstrated how inferences are highly sensitive to the priors. Rather than attempt to infer the true $\lambda$ posterior, we here compute the relative change to $\lambda$ when new experimental/observational evidence is introduced. By simulating posterior distributions and resulting entropic information gains, we compare three experimental pressures on $\lambda$: 1) evidence for an earlier start to life; $t_{\mathrm{obs}}$; 2) constraints on spontaneous abiogenesis from the lab; and 3) an exoplanet survey for biosignatures. First, we find that experiments 1 and 2 can only yield lower limits on $\lambda$, unlike 3. Second, evidence for an earlier start to life can yield negligible information on $\lambda$ if $t_{\mathrm{obs}} \ll \lambda_{\mathrm{max}}^{-1}$. Vice versa, experiment 2 is uninformative when $\lambda_{\mathrm{max}} \gg t_{\mathrm{obs}}^{-1}$. Whilst experiment 3 appears the most direct means of measuring $\lambda$, we highlight that early starts inform us of the conditions of abiogenesis, and that lab experiments could succeed in building new life. Together then, the three experiments are complimentary and we encourage activity in all to solve this grand challenge.