A Hadean timeline for the emergence of the RNA World.

Estimates for when life emerged on Earth range from ca. 3.8 Ga (Eoarchean) to the Hadean eon (≥4.0-4.5 Ga). Here, we conclude that a proposed early stage of life - the RNA World - appeared at ca. 4.33 Ga by tracking the near-surface thermal stability of key biomolecules comprising postulated RNA organisms. We apply a global three-dimensional numerical model to analyse the thermal evolution profile of Hadean crust in response to late accretion bombardment. Results show that frequent global sterilization events persisted up until about 4.4 Ga owing to hot ejecta deposition, rock vapour condensation, and enhanced geothermal gradients. Later, conditions became favorable to persistent biochemistry by supporting interconnected zones of biomolecule stability associated with extensive energy-rich hydrothermal oases. We identify an optimal time for the RNA World that dovetails with the emergence of the Last Universal Common Ancestor (LUCA) population.