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Extreme 15 N‐enrichments in 2.72‐Gyr‐old sediments: evidence for a turning point in the nitrogen cycle
Author(s) -
THOMAZO C.,
ADER M.,
PHILIPPOT P.
Publication year - 2011
Publication title -
geobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.859
H-Index - 72
eISSN - 1472-4669
pISSN - 1472-4677
DOI - 10.1111/j.1472-4669.2011.00271.x
Subject(s) - biogeochemical cycle , denitrification , nitrogen cycle , isotopes of nitrogen , environmental chemistry , nitrogen , nitrification , organic matter , nitrogen fixation , sedimentary depositional environment , chemistry , early earth , earth science , geochemistry , geology , paleontology , organic chemistry , structural basin
Although nitrogen is a key element in organic molecules such as nucleic acids and proteins, the timing of the emergence of its modern biogeochemical cycle is poorly known. Recent studies on the antiquity of the nitrogen cycle and its interaction with free oxygen suggests the establishment of a complete aerobic N biogeochemical cycle with nitrification, denitrification, and nitrogen fixation at about 2.68 Gyr. Here, we report new bulk nitrogen isotope data for the 2.72 billion‐year‐old sedimentary succession of the Tumbiana Formation (Pilbara Craton, Western Australia). The nitrogen isotopic compositions vary widely from +8.6‰ up to +50.4‰ and are inversely correlated with the very low δ 13 C values of associated organic matter defining the Fortescue excursion (down to about −56‰). We propose that this 15 N‐enrichment records the onset of nitrification coupled to the continuous removal of its derivatives (nitrite and nitrate) by denitrification. This finding implies an increase in the availability of electron acceptors and probably oxygen in the Tumbiana depositional environment, 300 million years before the oxygenation of the Earth’s atmosphere.