Abstract
The early start to life naively suggests that abiogenesis is a rapid process on Earth-like planets. However, if evolution typically takes ∼4 Gyr to produce intelligent life-forms like us, then the limited lifespan of Earth’s biosphere (∼5–6 Gyr) necessitates an early (and possibly highly atypical) start to our emergence—an example of the weak anthropic principle. Our previously proposed objective Bayesian analysis of Earth’s chronology culminated in a formula for the minimum odds ratio between the fast and slow abiogenesis scenarios (relative to Earth’s lifespan). Timing from microfossils (3.7 Gya) yields 3:1 odds in favor of rapid abiogenesis, whereas evidence from carbon isotopes (4.1 Gya) gives 9:1, both below the canonical threshold of “strong evidence” (10:1). However, the recent result of a 4.2 Gya LUCA pushes the odds over the threshold for the first time (nominally 13:1). In fact, the odds ratio is >10:1 for all possible values of the biosphere’s ultimate lifespan and speculative hypotheses of ancient civilizations. For the first time, we formally have strong evidence that favors the hypothesis that life rapidly emerges in Earth-like conditions (although such environments may themselves be rare).
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