Quantifying Habitability of the Hadean Earth: Impacts, Hydrothermal Systems, and Windows for Life's Emergence

Impacts during the Hadean heavy bombardment profoundly influenced Earth's early habitability, both frustrating and fostering conditions for life's origin through sterilization events and the creation of hydrothermal habitats. This study quantifies probabilistic "sweet-spot" windows for prebiotic chemistry and life's emergence, integrating impact-induced thermal perturbations with biochemical stability constraints in a comprehensive modeling framework.

We employ a well-tested three-dimensional numerical thermal model to simulate heat delivery to Earth's crust from asteroid impacts during late accretion (4.5–3.5 Ga). Simulations incorporate initial magma ocean scenarios, evolving crustal formation, and decreasing geothermal gradients. Bombardment parameters, including mass flux and size distributions, are derived from recent dynamical models informed by geochronology and geochemistry. Model outputs are validated against the Hadean zircon age spectra, providing constraints on impact flux and thermal history.

From these simulations, we calculate global habitable volumes, delineate coherent hydrothermal zones with steep thermal gradients conducive to prebiotic synthesis, quantify impact-driven localized sterilization, and apply Bayesian optimization for probabilistic "sweet-spot" analysis. Integrating hydrothermal activity, sterilization statistics, and thermal limits for biomolecule stability (e.g., RNA, proteins), we identify an optimal window for life's origin between approximately 4.4 and 4.3 Ga, postdating peak bombardment yet leveraging impact-generated habitats.

These findings highlight impacts' dual role in delaying yet enabling early life, align with emerging evidence for hydrothermal vents as cradles of biogenesis and recent molecular biology estimates placing the microbial community of the Last Universal Common Ancestor (LUCA) at ca. 4.2 Ga (4.09 - 4.33 Ga), and offer new insights into habitability of the Hadean Earth.