Deep Mantle-Atmosphere Coupling And Carbonaceous Bombardment: Options For Biomolecule Formation On Aan Oxidized Early Earth

Understanding what environmental conditions prevailed on early Earth during the Hadean eon, and how this set the stage for the origins of life, remains a challenge.

Geologic processes such as serpentinization and bombardment by chondritic material during the late veneer might have been very active, shaping an atmospheric composition reducing enough to allow efficient photochemical synthesis of HCN, one of the key precursors of prebiotic molecules.

HCN can rain out and accumulate in warm little ponds (WLPs), forming prebiotic molecules such as nucleobases and the sugar ribose. These molecules could condense to nucleotides, the building blocks of RNA molecules, one of the ingredients of life. Here, we perform a systematic study of potential sources of reducing gases on Hadean Earth and calculate the concentrations of prebiotic molecules in WLPs based on a comprehensive geophysical and atmospheric model.

We find that in a reduced H₂-dominated atmosphere, carbonaceous bombardment can produce enough HCN to reach maximum WLP concentrations of ∼1−10mM for nucleobases and, in the absence of seepage, ∼10−100μM for ribose. If the Hadean atmosphere was initially oxidized and CO₂-rich (90%), we find serpentinization alone can reduce the atmosphere, resulting in WLP concentrations of an order of magnitude lower than the reducing carbonaceous bombardment case.

In both cases, concentrations are sufficient for nucleotide synthesis, as shown in experimental studies. RNA could have appeared on Earth immediately after it became habitable (about 100Myr after the Moon-forming impact), or it could have (re)appeared later at any time up to the beginning of the Archean.

The “HCN machine”: Geological, atmospheric, meteoritic, and chemical processes synthesizing the building blocks of life on the Hadean Earth (artist’s impression, own creation, © Klaus Paschek). Panel A (lower right): Serpentinization and mantle processes lead to the efficient synthesis of H₂ and CH₄, including reactions with water and CO₂. Panel B (lower left): Emission of H₂, CH₄, and CO₂ from hydrothermal vents at volcanically active mid-ocean ridges. Panel C (center left): Degassing of H₂ and HCN by giant impacts. Panel D (top right): Synthesis of HCN from CH₄ and N₂ by UV photochemistry in the atmosphere. Panel E (top left): Atmospheric HCN rains out to the Earth’s surface and enters lakes, ponds, and the ocean. In ponds, wet-dry cycling and aqueous chemistry convert HCN into nucleobases, sugars, and ultimately RNA (oligo)nucleotides, key ingredients of life. — astro-ph.EP

Klaus Paschek, Thomas K. Henning, Karan Molaverdikhani, Yoshinori Miyazaki, Ben K. D. Pearce, Ralph E. Pudritz, Dmitry A. Semenov

Comments: Accepted for publication in The Astrophysical Journal. 44 pages, 12 figures (all colored)
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Atmospheric and Oceanic Physics (physics.ao-ph); Chemical Physics (physics.chem-ph)
Cite as: arXiv:2503.15479 [astro-ph.EP] (or arXiv:2503.15479v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2503.15479
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Submission history
From: Klaus Paschek
[v1] Wed, 19 Mar 2025 17:55:40 UTC (19,166 KB)
https://arxiv.org/abs/2503.15479
Astrobiology, Astrochemistry,