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Nitrogen Isotopic Composition and Density of the Archean Atmosphere

Science  04 Oct 2013:
Vol. 342, Issue 6154, pp. 101-104
DOI: 10.1126/science.1240971

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Same As It Ever Was

Nitrogen constitutes approximately 78% by volume of Earth's atmosphere and is a key component in its chemical and physical characteristics. It is not clear whether N2 has been so abundant throughout Earth's geological history. Marty et al. (p. 101, published online 19 September) analyzed the isotopic compositions of nitrogen and argon from fluid inclusions trapped in hydrothermal quartz formed 3 to 3.5 billion years ago. The partial pressure and isotopic composition of atmospheric N2 were similar to today's. Thus, other factors are needed to explain why liquid water existed on Earth's surface despite the Sun being 30% less luminous.

Abstract

Understanding the atmosphere’s composition during the Archean eon is fundamental to unraveling ancient environmental conditions. We show from the analysis of nitrogen and argon isotopes in fluid inclusions trapped in 3.0- to 3.5-billion-year-old hydrothermal quartz that the partial pressure of N2 of the Archean atmosphere was lower than 1.1 bar, possibly as low as 0.5 bar, and had a nitrogen isotopic composition comparable to the present-day one. These results imply that dinitrogen did not play a significant role in the thermal budget of the ancient Earth and that the Archean partial pressure of CO2 was probably lower than 0.7 bar.

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