Origin & Evolution of Life

Beyond Mediocrity: How Common is Life?

By Keith Cowing

Status Report

astro-ph.EP

May 9, 2023

Filed under abiogenesis, astro-ph.EP, astrobiology, exobiology, origin of life

Beyond Mediocrity: How Common is Life? — Figure 1 (top) The posterior cumulative distribution function (CDF) of 𝑝𝐿 (the probability of abiogenesis), given the evidence that life exists on Earth, computed from (4). The CDF is a function of the number of habitable worlds (𝑁𝐻 ) in the Milky Way. For reference, the horizontal line represents a cumulative probability of 0.05 and ties in directly with Table 1. Figure 2. (bottom) The posterior cumulative distribution function (CDF) of 𝑝𝐿 (the probability of abiogenesis), given the evidence that life exists on Earth, computed from (4). The CDF is a function of the number of habitable worlds (𝑁𝐻 ) in the Milky Way. For reference, the horizontal line represents a cumulative probability of 0.05 and ties in directly with Table 1. — astro-ph.EP)

The probability that life spontaneously emerges in a suitable environment (abiogenesis) is one of the major unknowns in astrobiology. Assessing its value is impeded by the lack of an accepted theory for the origin of life, and is further complicated by the existence of selection biases.

Appealing uncritically to some version of the “Principle of Mediocrity” — namely, the supposed typicality of what transpired on Earth — is problematic on empirical or logical grounds. In this paper, we adopt a Bayesian statistical approach to put on rigorous footing the inference of lower bounds for the probability of abiogenesis, based on current and future evidence.

We demonstrate that the single datum that life has appeared at least once on Earth merely sets weak constraints on the minimal probability of abiogenesis. In fact, the {\it a priori} probability assigned to this event (viz., optimistic, pessimistic or agnostic prior) exerts the strongest influence on the final result.

We also show that the existence of a large number of habitable worlds does not necessarily imply, by itself, a high probability that life should be common in the universe. Instead, as delineated before, the choice of prior, which is subject to uncertainty (i.e., admits multiple scenarios), strongly influences the likelihood of life being common.

If habitable worlds are uncommon, for an agnostic prior, a deterministic scenario for the origin of life might be favoured over one where abiogenesis is a fluke event.

Amedeo Balbi, Manasvi Lingam

Comments: 7 pages, 2 figures. Published in MNRAS
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM); Populations and Evolution (q-bio.PE)
Cite as: arXiv:2305.05395 [astro-ph.EP] (or arXiv:2305.05395v1 [astro-ph.EP] for this version)
Journal reference: Monthly Notices of the Royal Astronomical Society, Volume 522, Issue 2, June 2023, Pages 3117-3123
Related DOI:
https://doi.org/10.1093/mnras/stad1155
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Submission history
From: Amedeo Balbi
[v1] Tue, 9 May 2023 12:42:21 UTC (168 KB)
https://arxiv.org/abs/2305.05395
Astrobiology

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

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