Early plate tectonics, pyrophosphate, Na+, and the origin of life
2011 (English)In: Origins2011 International Conference / [ed] Muriel Gargaud & Robert Pascal, Montpellier, 2011Conference paper (Other academic)
Life may have started in association with early plate tectonic processes. Considerable geological evidence supports an initiation of plate tectonics on Earth shortly after the end of the Hadean about 4 Ga ago. The salinity of the young ocean was probably high, since sodium is rapidly mobilized from rocks by hydrothermal processes. Such processes also lead to the continuous release of Mg2+ and precipitation of brucite, Mg(OH)2, during serpentinization of olivine in mafic rocks of the ocean floor. The serpentinization processes are now recognized as probably the most important metamorphic hydration reactions that may contribute to our understanding of the origin of life, since they are coupled to the formation of source molecules like H2, thought to have been required for the origin of life. The transformation of olivine at relatively low temperature (50-300°C) to the serpentine mineral lizardite as the prevalent phase is particularly associated with reduction of water to hydrogen and oxidation of Fe(II) to Fe(III). During weathering of olivine and pyroxene in mafic rocks Fe(OH)2 may be formed as an intermediate phase (in solid solution with Mg(OH)2)during the partial oxidation of Fe(II). Fe(OH)2 is metastable with respect to magnetite and will convert to this mineral via a spontaneous reaction. However, the conversion also creates a small amount of native iron, which means that the ocean floor is quite reducing. The oceanic crust is hydrated to a depth of a kilometer or more and can therefore provide a substantial flux of water for serpentinization of upper mantle rocks when it is subducted. A modern hydrothermal environment in which Na+ and Mg2+ are abundant exists in sediment-starved alkaline subduction zones, like the Mariana forearc in the western Pacific Ocean. It is considered to mimic the Archean Earth. Pyrophosphate could have been formed during early subduction of oceanic lithosphere by dehydration of protonated orthophosphates. The key to pyrophosphate formation in these geological environments is low water to rock ratio, i.e. low local activity of water. The difference in complexity between the inorganic pyrophosphate and ATP also supports the possible role of PPi as early energy donor for the origin of life.
Place, publisher, year, edition, pages
Other Natural Sciences
IdentifiersURN: urn:nbn:se:su:diva-65255OAI: oai:DiVA.org:su-65255DiVA: diva2:461934
International Conference for the Study of the Origin of Life