When did Life Likely Emerge on Earth in an RNA-First Process?

Abstract

The widespread presence of ribonucleic acid (RNA) catalysts and cofactors in Earth's biosphere today suggests that RNA was the first biopolymer to support Darwinian evolution. However, most "path-hypotheses" to generate building blocks for RNA require reduced nitrogen-containing compounds not made in useful amounts in the CO2-N2-H2O atmospheres of the Hadean. We review models for Earth's impact history that invoke a single ~10^23 kg impactor (Moneta) to account for measured amounts of platinum, gold, and other siderophilic ("iron-loving") elements on the Earth and Moon. If it were the last sterilizing impactor, Moneta would have reduced the atmosphere but not its mantle, opening a "window of opportunity" for RNA synthesis, a period when RNA precursors rained from the atmosphere to land holding oxidized minerals that stabilize advanced RNA precursors and RNA. Surprisingly, this combination of physics, geology, and chemistry suggests a time when RNA formation was most probable, ~120 +/- 100 million years after Moneta's impact, or ~4.36 +/- 0.1 billion years ago. Uncertainties in this time are driven by uncertainties in rates of productive atmosphere loss and amounts of sub-aerial land.

Paper accepted to ChemSystemsChem [https://onlinelibrary.wiley.com/journal/25704206] August 22, 2019

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• Towards RNA life on Early Earth: From atmospheric HCN to biomolecule production in warm little ponds
• An Objective Bayesian Analysis of Life's Early Start and Our Late Arrival
• Laboratory studies on the viability of life in H${}_2$-dominated exoplanet atmospheres
• Geoastronomy: Rocky planets as the Lavosier-Lomonosov Bridge from the non-living to the living world