Origin of Life

Theories and evidence for chemical biopoieses

Hydrothermal vents

ScienceDirect - Trends in Biochemical Sciences : The rocky roots of the acetyl-CoA pathway: "Geologists have suggested that life might have emerged at hydrothermal vents, chemists have shown that metal sulphides such as FeS and NiS can catalyse biochemical reactions in the absence of proteins, and biologists have suggested that the acetyl-coenzyme-A (CoA) pathway of CO2 fixation might be very ancient. New findings from the enzymes at the heart of the acetyl-CoA pathway, carbon monoxide dehydrogenase (CODH) and acetyl-CoA synthase (ACS), indicate that metals and metal sulphides do the biochemical work of CO2 fixation. Here we propose that biochemistry got started when the two volatiles that were thermodynamically furthest from equilibrium on the early Earth -- namely, marine CO2 from volcanoes and hydrothermal H2 -- met at a hydrothermal vent rich in metal sulphides. In this 'hydrothermal reactor' hypothesis, a primitive, inorganically catalysed analogue of the exergonic acetyl-CoA pathway, using H2 as the initial electron donor and CO2 as the initial acceptor, was instrumental in the synthesis of organic precursors to fuel primordial biochemical reactions. We suggest that primordial biochemistry was housed in an acetate-producing hydrothermal reactor that retained reduced carbon compounds produced within its naturally forming inorganic confines."Michael J. Russell and William Martin, The rocky roots of the acetyl-CoA pathway Trends in Biochemical Sciences Volume 29, Issue 7 , July 2004, Pages 358-363

Hydrothermal simulation experiments as a tool for studies of the origin of life on Earth and other terrestrial planets: a review. : "The potential of life's origin in submarine hydrothermal systems has been evaluated by a number of investigators by conducting high temperature-high pressure experiments involving organic compounds. In the majority of these experiments little attention has been paid to the importance of constraining important parameters, such as the pH and the redox state of the system. This is particularly revealed in the apparent difficulties in interpreting experimental data from hydrothermal organic synthesis and stability studies. However, in those cases where common mineral assemblages have been used in an attempt to buffer the pH and redox conditions to geologically and geochemically realistic values, theoretical and experimental data seem to converge. The use of mineral buffer assemblages provides a convenient way by which to constrain the experimental conditions. Studies at high temperatures and pressure in the laboratory have revealed a number of reactions that proceed rapidly in hydrothermal fluids, including the Strecker synthesis of amino acids. In other cases, the verification of postulated abiotic reaction mechanisms has not been possible, at least for large molecules such as large fatty acids and hydrocarbons. This includes the Fischer-Tropsch synthesis reaction. High temperature-high pressure experimental methods have been developed and used successfully for a long time in, for example, mineral solubility studies under hydrothermal conditions. By taking advantage of this experimental experience new and, at times, unexpected directions can be taken in bioorganic geochemistry, one being, for instance, primitive two-dimensional information coding. This article critically reviews some of the organic synthesis and stability experiments that have been conducted under simulated submarine hydrothermal conditions. We also discuss some of the theoretical and practical considerations that apply to hydrothermal laboratory studies of organic molecules related to the origin of life on Earth and probably also to the other terrestrial planets."
Holm NG, Andersson E. Hydrothermal simulation experiments as a tool for studies of the origin of life on Earth and other terrestrial planets: a review. Astrobiology. 2005 Aug;5(4):444-60.

Nitrogen reduction under hydrothermal vent conditions: implications for the prebiotic synthesis of C-H-O-N compounds. : "Dinitrogen is reduced in dilute hydrogen sulfide (H2S) solutions to ammonium at 120 degrees C. Experiments with dissolved dinitrogen (partial pressure 50 bar) in a 12 x 10(-3) mol/L H2S(aq) solution yield approximately 10(-5) mol/L NH4+ within 2-7 days. These yields are consistent with the equilibrium NH4+ concentration for the N-S-H system under these conditions. The formation of ammonium is catalyzed by the presence of freshly precipitated iron monosulfide. These results indicate that dinitrogen can be reduced at moderate temperatures in hydrothermal vent systems. Abiotic nitrogen reduction could have taken place within primordial hydrothermal vents, supplying some ammonia for the synthesis of C-H-O-N compounds via abiotic processes. The yield of ammonia via dinitrogen reduction by hydrogen sulfide, however, is so low that it is doubtful this process could have produced enough ammonia to sustain prebiotic hydrothermal synthesis of C-H-O-N compounds in or around vent systems."
Schoonen MA, Xu Y. Nitrogen reduction under hydrothermal vent conditions: implications for the prebiotic synthesis of C-H-O-N compounds. Astrobiology. 2001 Summer;1(2):133-42.


Anonymous Anonymous said...

If the PubMed link takes you to the Search page rather than the article, simply copy and paste the Title.

12:06 PM  

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