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Ammonia on the prebiotic Earth: Iron(II) reduction of nitriteTheories for the origin of life require the availability of reduced nitrogen. In the non-reducing atmosphere suggested by geochemical evidence, production in the atmosphere and survival of NH3 against photochemical destruction are problematic. Electric discharges and impact shocks would produce NO rather than HCN or NH3. Conversion of NO to nitrous and nitric acid (by way of HNO) and precipitation in acid rain would provide a source of fixed nitrogen to the early ocean. One solution to the NH3 problem may have been the reduction of nitrite/nitrate in the ocean with aqueous ferrous iron, Fe(2+): 6Fe(+2) + 7 H2O + NO2(-) yields 3Fe2O3 + 11 H(+) + NH3. We have measured the kinetics of this reaction as a function of temperature, pH, and concentrations of salts, Fe(+2), and NO2(-). Cations (Na(+), Mg(2+), K(+)) and anions (Cl(-), Br(-), SO4(2-)) increase the rate by factors of 4 to 8. Although a competing pathway yields N2, the efficiency of the conversion of nitrite to ammonia ranges from 25% to 85%. Nitrate reduction was not consistently reproducible; however, when it was observed, its rate was slower by at least 8X than that of nitrite reduction. If the prebiotic atmosphere contained 0.2 to 10 atmospheres CO2 as suggested by Walker (1985), the Fe(+2) concentration and the rate would have been limited by siderite (FeCO3) solubility.
Document ID
19950032158
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Summers, David P.
(NASA Ames Research Center Moffett Field, CA, US, United States)
Chang, Sherwood
(NASA Ames Research Center Moffett Field, CA, US, United States)
Date Acquired
August 16, 2013
Publication Date
June 1, 1994
Publication Information
Publication: Origins of Life and Evolution of the Biosphere
Volume: 24
Issue: 2-4
ISSN: 0169-6149
Subject Category
Life Sciences (General)
Accession Number
95A63757
Distribution Limits
Public
Copyright
Other

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