In 2000, a completely new kind of vent system was discovered at mid-Atlantic ocean that differ significantly from black-smokers and never seen before chemical enviroment. They are characterized by carbonate chimneys that rise up to 60 meters (picture below). The system, named Lost City hydrothermal field (LCHF) could also be a spot for origins. They are also located a few kilometers away from the spreading
zone. They fluids are heated up a ~ 200°C, but they are not in close contact with the magma chamber like a black-smoker. Instead they are fueled by chemical reactions between mantle rocks and seawater. The rocks contain large amounts of olivine (a Mg-Fe silicate) which reacts with seawater at temperatures ~200°C and forms serpentine minerals (hydrous Mg-silicates) and magnetite. This process, referred to as serpentinization makes the system highly alkaline (pH 9–11). An interesting fact is that, serpentinization have been producing geological H2 for as long as there has been water on the Earth. This new system, has yet to get an experimental focus for origin of life studies, although i do think they are researchers whom are looking in this idea. Do keep an eye on this.
In the next post i will be reviewing some of the hydrothermal vent simulators i have used in the past for origin of life based experiments.
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Miller and Urey both designed their experiment assuming that the primitive atmosphere was reducing. This was a valid assumption at that time, and organic compounds are formed better in a reducing conditions. However, this reducing atmosphere scenario has changed, most scientist nowadays would envision a more redox neutral atmosphere. This is because there are no evidences of a reducing atmosphere documented in the rocks[1,2,3]. However, there is a small chance that a reduced atmosphere could happen for a short period of time in the presence of a meteorites impact or vapors from an erupting volcano. Also it is worth noting, because there is lack of ozone layers during those periods, UV rays could have destroyed the biomolecules in the atmosphere as soon as they are formed. All this leads that the prebiotic atmosphere is limited in the sense of origins; moreover this biomolecules needs to be protected by the UV rays ; hence a SHSs’ reducing powers and its UV cloaking ability makes them an ideal spot for origins. The reducing conditions in hydrothermal vents (before the discovery of Lost City Hydrothermal field) is fueled by it reduced minerals which could act as a template for various catalytic activity [6,7,8,9,10] including polymerization.
SHS is also the only place that primitive life forms could have been protected during an event of meteorite shower and/or partial vaporization of the ocean. Although, SHS could well be a spot for origins, critics often cite that residence times in axial hydrothermal environments range from years to decades, ( in other word, the time spent by fluid in the hydrothermal vents is long) while those in lower temperature off-axis diffuse flow systems may be on the order of thousands of years. These residence times are impossible to model experimentally, the effects of long residence times in SHSs are not generally considered in SHS experiments. This is one of the major limitation for experiments on SHS simulation.
1. Lambert, I.B, Donnelly, T.H, Dunlop, J.S.R and Groves, D.I (1978) Stable Isotope Compositions of Early Archaean Sulphate Deposits of Probable Evaporitic and Volcanogenic Origins: Nature, v.276,p.808.
2. Dimroth, E and Kimberley, M.M (1976) Precambrian Atmospheric Oxygen: Evidence in the Sedimentary Distributions of Carbon, Sulfur, Uranium and Iron: Canadian Journal Earth Science, v.13,1976, pp.1161-l185.
3. Zeschke, G (1960) Transportation of Uraninite in the Indus River, Pakistan: Geological Society of South Africa v.63, p.87.
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5. Sleep, N. H, Zahnle, K. J, Kasting, L F and Morowitz, H.J (1989) Annihilation of ecosystems by large asteroid impacts on the early Earth, Nature 342, 139-142.
6. Wachtershauser, G (1988) Before enzymes and templates: Theory of surface metabolism, Microbiology Review. 52, 452-484.
7. Wachtershauser, G (1988) Pyrite formation, the first energy source for life: A hypothesis, Systematic and Applied Microbiology 10, 207-210.
8. Wachtershauser, G (1990) The case for the chemoautotrophic origin of life in an iron- sulfur world, Origins of Life and Evolution of the Biosphere 20, 173-176
9. Russell, M. J, Hall, A. J and Turner, D (1989) In vitro growth of iron sulphide chimneys: Possible culture chambers for origin-of-life experiments, Terra Nova 1, 238-241
10. Kadko, D and Butterfield, D.A (1998) The relationship of hydrothermal fluid composition and crustal residence time to the maturity of vent fields on the Juan de Fuca Ridge. Geochimica et Cosmochimica Acta 62:1521– 1533
11. Turekian, K.K, Cochran, J.K (1986) Flow-rates and reaction-rates in the Galapagos Rise spreading center hydrothermal system as inferred from Ra-228/Ra-226 in vesicomyid clam shells. Proceedings of the National Academy of Sciences of the United States of America, 83:6241–6244
12. Johnson, H.P, Pruis, M.J (2003) Fluxes of fluid and heat from the oceanic crustal reservoir. Earth and Planetary Science Letters 216:565–574
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