The geochemical modelling of emergent life from submarine hydrothermal environments
Hydrothermal systems may have been more widespread in the Hadean due to a greater heat flux. To investigate this possibility, and unravel the mechanism(s) by which the pH of high-temperature vent fluids become acidic and what produces their distinctive black colour, reactions between model seawater and mafic/ultramafic rock were conducted. Results indicated that ancient, medium to high temperature (150-300°C), alkaline hydrothermal fluids would have precipitated carbonates, brucite, and calcite upon re-mixing with cold, slightly alkaline seawater and may have predominated in the Hadean. Acid pH was effected by the loss of magnesium from seawater and calcium loss from mafic rock. Black-smokers were unlikely in the Hadean as the ocean was probably acidic due to high levels of CO2. Water-rock reaction models were constructed to test the possibility that simple amino acids could have been generated in early hydrothermal fluids, and to see how pH and redox conditions affect their distribution (cf. Amend and Shock, 1998). Though concentrations of amino acids produced were negligible, amino acids were stable in low-temperature, alkaline, and reduced hydrothermal fluids and may have concentrated in the colloidal sieve comprising a hydrothermal mound. An extension of the experiment to determine if glycine could be condensed to higher carbon number amino acids (alanine, valine, leucine) under hydrothermal conditions, indicated that condensation may be 'pulled' by a decrease of H2O activity of the fluid. In conclusion, this study improved on previous environmental and reactant constraints by simulating the generation of inorganic prebiotic reactants from the local geochemical hydrothermal environment. Consequently, the quantity of chemical species such as hydrogen and sulfide available for organic synthesis were limited by the local geochemical settings in the model, whereas others have, often admittedly, used reactants in higher concentrations than were probably available when Life emerged.