Open AccessExperimental dissolution of molybdenum‐sulphides at low oxygen concentrations: A first‐order approximation of late Archean atmospheric conditions
Author(s) -
Greber Nicolas D.,
Mäder Urs,
Nägler Thomas F.
Publication year - 2015
Publication title -
earth and space science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.843
H-Index - 23
ISSN - 2333-5084
DOI - 10.1002/2014ea000059
Subject(s) - atmospheric oxygen , dissolution , molybdenum , oxygen , isotopes of oxygen , atmosphere (unit) , environmental chemistry , hydrothermal circulation , geology , archean , mineralogy , chemistry , geochemistry , inorganic chemistry , physics , meteorology , organic chemistry , seismology
The abundance of atmospheric oxygen and its evolution through Earth's history is a highly debated topic. The earliest change of the Mo concentration and isotope composition of marine sediments are interpreted to be linked to the onset of the accumulation of free O 2 in Earth's atmosphere. The O 2 concentration needed to dissolve significant amounts of Mo in water is not yet quantified, however. We present laboratory experiments on pulverized and surface‐cleaned molybdenite (MoS 2 ) and a hydrothermal breccia enriched in Mo‐bearing sulphides using a glove box setup. Duration of an experiment was 14 days, and first signs of oxidation and subsequent dissolution of Mo compounds start to occur above an atmospheric oxygen concentration of 72 ± 20 ppmv (i.e., 2.6 to 4.6 × 10 −4 present atmospheric level (PAL)). This experimentally determined value coincides with published model calculations supporting atmospheric O 2 concentrations between 1 × 10 −5 to 3 × 10 −4 PAL prior to the Great Oxidation Event and sets an upper limit to the molecular oxygen needed to trigger Mo accumulation and Mo isotope variations recorded in sediments. In combination with the published Mo isotope composition of the rock record, this result implies an atmospheric oxygen concentration prior to 2.76 Ga of below 72 ± 20 ppmv.