  Mechanisms of nucleic acid accumulation were likely critical to the emergence
of life in the ferruginous oceans of the early Earth. How exactly prebiotic
geological settings accumulated nucleic acids from dilute aqueous solutions, is
poorly understood. As a possible solution to this concentration problem, we
simulated the conditions of prebiotic low-temperature alkaline hydrothermal
vents in co-precipitation experiments to investigate the potential of
ferruginous chemical gardens to accumulate nucleic acids via sorption. The
injection of an alkaline solution into an artificial ferruginous solution under
anoxic conditions (O2 <0.01% of present atmospheric levels) and at ambient
temperatures, caused the precipitation of amakinite (white rust), which quickly
converted to chloride-containing fougerite (green rust). RNA was only
extractable from the ferruginous solution in the presence of a phosphate
buffer, suggesting RNA in solution was bound to Fe2+ ions. During chimney
formation, this iron-bound RNA rapidly accumulated in the white and green rust
chimney structure, as it was depleted from the surrounding solution. Our
findings reveal that in the oceans of the early Earth, white and green rust
chimneys were likely key geochemical features that can rapidly sequester and
accumulate RNA. This represents a new mechanism for nucleic acid accumulation,
in addition to wet dry cycles, and may have promoted RNA survival in a dilute
prebiotic ocean.
