Origin & Evolution of Life

Towards RNA Life On Early Earth: From Atmospheric HCN To Biomolecule Production In Warm Little Ponds

By Keith Cowing
January 4, 2022
Filed under
Towards RNA Life On Early Earth: From Atmospheric HCN To Biomolecule Production In Warm Little Ponds
The origin of life on Earth involves the early appearance of an information-containing molecule such as RNA.

The basic building blocks of RNA could have been delivered by carbon-rich meteorites, or produced in situ by processes beginning with the synthesis of hydrogen cyanide (HCN) in the early Earth’s atmosphere.

Here, we construct a robust physical and non-equilibrium chemical model of the early Earth atmosphere. The atmosphere is supplied with hydrogen from impact degassing of meteorites, sourced with water evaporated from the oceans, carbon dioxide from volcanoes, and methane from undersea hydrothermal vents, and in which lightning and external UV-driven chemistry produce HCN.

This allows us to calculate the rain-out of HCN into warm little ponds (WLPs). We then use a comprehensive sources and sinks numerical model to compute the resulting abundances of nucleobases, ribose, and nucleotide precursors such as 2-aminooxazole resulting from aqueous and UV-driven chemistry within them. We find that at 4.4 bya (billion years ago) peak adenine concentrations in ponds can be maintained at ~2.8μM for more than 100 Myr.

Meteorite delivery of adenine to WLPs produce similar peaks in concentration, but are destroyed within months by UV photodissociation, seepage, and hydrolysis. The early evolution of the atmosphere is dominated by the decrease of hydrogen due to falling impact rates and atmospheric escape, and the rise of oxygenated species such as OH from H2O photolysis. Our work points to an early origin of RNA on Earth within ~200 Myr of the Moon-forming impact.

Ben K. D. Pearce, Karan Molaverdikhani, Ralph E. Pudritz, Thomas Henning, Kaitlin E. Cerrillo

Comments: Accepted to ApJ, 27 pages (14 main text), 11 figures, 9 tables
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Atmospheric and Oceanic Physics (physics.ao-ph); Chemical Physics (physics.chem-ph); Computational Physics (physics.comp-ph); Geophysics (physics.geo-ph)
Cite as: arXiv:2201.00829 [astro-ph.EP] (or arXiv:2201.00829v1 [astro-ph.EP] for this version)
Submission history
From: Ben K. D. Pearce
[v1] Mon, 3 Jan 2022 19:00:04 UTC (6,780 KB)

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