Timing Earth's Abiotic Kitchen: Short Hydrothermal Fluid Residence Times in Serpentinizing Oceanic Crust

Abstract

Hydrothermal alteration of ultramafic rock (serpentinization) creates extremely reducing (H2-rich) fluids in the oceanic crust, resulting in strong thermodynamic drives to reduce CO2 to organic molecules in the absence of life. Timescales on which such hydrothermal fluids circulate (thus produce or destroy such organic molecules) have remained enigmatic. In their new publication, Moore et al. (2021, https://doi.org/10.1029/2021JC017886) present compelling radioisotope-based estimates of fluid residence times in a widely known site of purported abiotic synthesis—The Lost City Hydrothermal Field. Using a model that accounts for the sorptive behavior of Ra radionuclides during circulation, they find that fluids at Lost City must have remarkably short residence times, averaging 0.5–2 years or less. The study represents a critical step forward in our understanding of Earth's abiotic organic “kitchen”, as it now places a constraint on the timeframe in which organic molecule creation should occur in such fluids (if at all) prior to venting at the seafloor.