Nitrogen Isotopic Composition and Density of the Archean Atmosphere

TL;DR

This study analyzes nitrogen and argon isotopes in ancient quartz to estimate the Archean atmosphere's nitrogen pressure and isotopic composition, revealing a lower nitrogen pressure and similar isotopic signature to today.

Contribution

It provides new constraints on the atmospheric composition of the Archean eon using isotopic analysis of fluid inclusions in ancient minerals.

Findings

PN2 was lower than 1.1 bar, possibly around 0.5 bar

Archean nitrogen isotopic composition similar to modern levels

Archean PCO2 was probably below 0.7 bar

Abstract

Understanding the atmosphere's composition during the Archean eon is a fundamental issue to unravel ancient environmental conditions. We show from the analysis of nitrogen and argon isotopes in fluid inclusions trapped in 3.0-3.5 Ga hydrothermal quartz that the PN2 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 PCO2 was probably lower than 0.7 bar.