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Nitrogen reduction in mafic rocks

Nitrogen reduction in mafic rocks. Nils Holm Department of Geology and Geochemistry Stockholm University. Flow of water through oceanic crust. Degens, 1989. Formation of the deepsea floor. Ferromagnesian minerals. Olivin e (Mg,Fe) 2 SiO 4 Pyroxenes Ca(Mg,Fe)Si 2 O 6 augite

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Nitrogen reduction in mafic rocks

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  1. Nitrogen reduction in mafic rocks Nils Holm Department of Geology and Geochemistry Stockholm University

  2. Flow of water through oceanic crust Degens, 1989

  3. Formation of the deepsea floor

  4. Ferromagnesian minerals Olivin e (Mg,Fe)2SiO4 Pyroxenes Ca(Mg,Fe)Si2O6 augite (Mg,Fe)SiO3 hypersthene Amfibole Ca2(Mg,Fe)5Si8O22(OH)2 hornblende

  5. Olivines at the foot of the Syrtis Major Volcano on Mars Hoefen et al., 2003

  6. Serpentinisation of olivine 2Mg1.8Fe0.2SiO4 + 3H2O = olivine Mg2.85 Fe0.15 Si2O5(OH)4 + Mg 0.75 Fe0.25 (OH)2 serpentine ferrobrucite (intermediate) 12Mg0.75Fe0.25(OH)2=Fe3O4+9Mg(OH)2+H2+2H20 ferrobrucite magnetitebrucite The reaction is characterised by high pH (modified from Bach et al., 2006)

  7. Two common redox buffer assemblages:

  8. Fischer-Tropsch synthesis The industrial process: CO + H2organic compounds In the presence of catalysts like Fe or ZnO +/- Fe2O3, Fe3O4, Cr2O3 ZnO+Cr2O3  linear alcohols ZnO+ Fe2O3  linear hydrocarbons In natural environments CO2 may be reduced to CO in the presence of native Fe and Ni Hägg, 1966

  9. Fischer-Tropsch Synthesis II In geochemistry the term Fischer-Tropsch synthesis is often (incorrectly) used to describe a direct mechanism for the formation of methane from carbon dioxide with magnetite as a catalyst: CO2 + H2 CH4 + 2H2O

  10. Is there methane on Mars?

  11. Ocean Drilling ProgramLeg 201 2002

  12. Dissolved NO3- in pore water of ODP Leg 201 ‘NO3- and NO2- are converted more rapidly to NH4+ than N2, particularly in the presence of Fe and Ni metal’ Smirnov et al., 2008

  13. Nitrite and nitrate is reduced to ammonium in the presence of native Fe and Ni Smirnov et al., 2008

  14. Edwards, Bach and McCollom, 2005

  15. The constituents of RNA(ribonucleic acid) From Schwartz, 1998

  16. HCN oligomers hydrolyze to amino acids and nitrogen bases All of the biologically important purines are present in reasonable amounts in carbonaceous meteorites, but only one pyrimidine (uracil) has been detected, and that in much lower concentration Stoks and Schwartz, 1979 From Ferris, 1984

  17. Evolution of the concentration of adenine at 300ºC Franiatte et al., 2008

  18. Hydrogen cyanide may be formed in a variety of ways • 2CH4 + N2 → 2HCN + 3H2 (1) • CO + NH3 → HCN + H2O (2) • CH4 + NH3 → HCN + 3H2 (3)

  19. Methane molecule adsorbed in the interlayer of montmorillonite Sposito et al., 1999

  20. Hydrothermal activity also occurs at convergent margins C. German

  21. Schematic cross-section of typical settings for mud volcanoes in Mariana forearc Fluids of the Conical Seamount have pH 12.6 and contain C1-C4 hydrocarbons and carboxylic acids and are enriched in boron (x10) and ammonia (Fryer et al., 1999)

  22. Fluid inclusions of Conical Seamount chimneys contain light and longer chain hydrocarbons, aromatics and acetate (Haggerty, 1991) Mariana Trench in the western Pacific Ocean (Mottl et al., 2003)

  23. Composition of the pore water from an ODP drill hole on South Chamorro Seamount Mottl et al., 2003

  24. Conclusions • In theory, it is possible to synthesize most of the constituents of nucleotides and proteins via a HCN pathway in hydrothermal environments • But, the origin of life is, perhaps, only possible on planets with some kind of plate tectonics

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