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Astrobiology

Title:		Nitrogen in Ancient Mud: A Biosignature?
Author(s):		Stueken EE;
Address:		"Department of Earth and Space Sciences and Astrobiology Program, University of Washington , Seattle, Washington, USA . Department of Earth Sciences, University of California , Riverside, California, USA . Department of Earth and Environmental Sciences, University of St Andrews , St Andrews, Scotland, UK"
Journal Title:		Astrobiology
Year:		2016
Volume:		20160901
Issue:		9
Page Number:		730 - 735
DOI:		10.1089/ast.2016.1478
ISSN/ISBN:		1557-8070 (Electronic) 1557-8070 (Linking)
Abstract:		"Nitrogen is an essential nutrient for all life on Earth and possibly elsewhere. Burial of nitrogen bound to organic matter constitutes the major flux of nitrogen into sediments today, which has led to the inference that nitrogen enrichments in sedimentary rocks may be a biosignature. However, abiotic processes such as lightning or volcanism can fix atmospheric N2 and contribute to sedimentary nitrogen burial in the absence of life. It is therefore uncertain whether observed nitrogen enrichments of up to 430 ppm in Paleoarchean metasedimentary biotite grains are indeed biogenic. This study seeks to address that problem with a numerical model. The NH4(+) concentration of an abiotic ocean is modeled as a function of source fluxes, pH-dependent NH3 volatilization, and equilibrated adsorption of NH4(+) onto clay particles. The results suggest that the observed nitrogen concentrations in Paleoarchean biotite can only be reconciled with purely abiotic processes if the ocean was more acidic (pH <6) and/or if the source fluxes from lightning and volcanism were at least an order of magnitude higher (>/=10(12) mol/yr) than previously thought. The bulk of the nitrogen is thus most likely of biological origin. While this does not necessitate a particular metabolism such as biological N2 fixation, the data provide evidence of nitrogen utilization back to 3.8 Gyr. Nitrogen abundances could thus provide useful information in extraterrestrial missions. KEY WORDS: Early Earth-Biosignatures-Nitrogen fixation. Astrobiology 16, 730-735"
Keywords:		"Adsorption Ammonium Compounds/analysis Geologic Sediments/*chemistry Models, Theoretical Nitrogen/*analysis *Origin of Life Time Factors;"
Notes:		"MedlineStueken, Eva E eng Research Support, U.S. Gov't, Non-P.H.S. 2016/09/02 Astrobiology. 2016 Sep; 16(9):730-5. doi: 10.1089/ast.2016.1478. Epub 2016 Sep 1"