Chiara Boschi, Andrea Dini , Gretchen L. Früh-Green , Luca Caricchi 

Biosignatures in the rock record limit the time available for life to start on Earth to 600-800 million years1 (4.5-3.7 Ga; Hadean-Archean). Whether the conditions for the synthesis of complex organic molecules were unique to this time or remain present today is unclear, but understanding these conditions is essential for the search of life on other planets. The outer portion of the Hadean Earth consisted of a thick mafic crust2,3 and the upper mantle from which the crust was extracted4. Here we show that the recycling of the Earth’s initial crust to produce the first continental crust5–8, resulted in extreme thinning of the initial mafic crust allowing the interaction between ocean water and the upper mantle at a global scale. This global hydrothermal reactor was similar to the present-day active “Lost City Hydrothermal Field”9, but extended on a planetary scale. The geological record indicates that the interaction between H2O and olivine-rich rocks resulted in the production of 5-20 vol.% brucite10–13, a key catalytic mineral for high temperature stabilisation, selection and phosphorylation of ribose14,15. The secular cooling of our planet16–18, the accretion of continental crust, and deposition of sediments progressively shut down the global reactor. These processes dramatically reduced the production of brucite and the probability of synthesizing prebiotic molecules. Our results suggest that the geodynamic evolution of planets should be considered when searching for life in the wider Universe.