Streamer Discharges in the Atmosphere of Primordial Earth.

The seminal Miller‐Urey experiment suggests that lightning may have contributed to the origin of life on Earth through the formation of amino acids and carbon acids. We here focus on the early stages of lightning in the atmosphere of Primordial Earth, so‐called streamer discharges. We discuss rate coefficients for electrons and study electron avalanches and avalanche‐to‐streamer transitions by modeling the motion of electrons with a 2.5 D particle‐in‐cell Monte Carlo code in the strongly reducing atmosphere used by Miller and Urey (MU) and the weakly reducing atmospheric suggested more recently (by Kasting (1993), https://doi.org/10.1126/science.11536547) for Earth 3.8 Ga ago and compare results with conditions on Modern Earth. Our simulations show that streamers incept at fields of 140–180 Td in Kasting's mixture and at fields of ≈114 Td in the MU mixture, thus their inception is more difficult in Kasting's mixture. Conclusively, discharges on Primordial Earth might have been more challenging to incept. Plain Language Summary: In the 1950s Miller and Urey performed discharge experiments in a gas mixture resembling the atmosphere of Ancient Earth and showed that a significant amount of prebiotic material was produced, possibly laying the foundation for the further synthesis of the first biomolecules. We perform numerical computer simulations of electron avalanches in the gas mixture used by Miller and Urey as well as in a mixture suggested more recently for the composition of Ancient Earth's atmosphere 3.8 Ga ago and study the conditions needed for the inception of filamentary discharges. We calculate electron and discharge properties and compare them with results for discharges on Modern Earth. We provide a table summarizing the electric fields needed for discharge inception in these different atmospheres. Our simulations show that discharges in the Miller‐Urey mixture incept at lower fields than in Kasting's mixture and partly on Modern Earth which implies that discharges in the atmosphere of Ancient Earth might have been more challenging to incept than previously thought. Key Points: We perform simulations of electron avalanches and streamers in different gas mixtures for Primordial and Modern EarthIonization rates are higher in strongly reducing gas mixtures, such as used by Miller and Urey, than in weakly reducing mixturesIn the Miller and Urey gas mixture streamers incept at ≈114 Td; in weakly reducing atmospheres, suggested by Kasting, at 140–180 Td [ABSTRACT FROM AUTHOR]