We present a new and innovative way of determining the oxygen level of Earth's past atmosphere by directly measuring inclusion gases trapped in halite. After intensive screening using multiple depositional, textural/fabric and geochemical parameters, tectonically undisturbed cumulate, chevron, and cornet halite inclusions may retain atmospheric gas during crystallization from shallow saline, lagoonal and/or saltpan brine. These are the first measurements of inclusion gas for the Neoproterozoic obtained from 815±15 m.y. old Browne Formation chevron halite of the Officer Basin, southwest Australia. The thirty-one gas measurements afford us a direct glimpse of the composition of the mid-late Neoproterozoic atmosphere and register an oxygen content of 10.9±1.4 %. The measured pO2 puts oxygenation of Earth's paleoatmosphere about 100 to 200 million years ahead of current models and proxy studies. It also puts oxygenation of the Neoproterozoic atmosphere in agreement with time of diversification of eukaryotes and in advance of the emergence of marine animal life.
We thank the Geological Survey of Australia for permission to sample the Empress 1A and Lancer 1 cores, the Natural Sciences and Engineering Research Council of Canada for financial support (grant #7961–15) of U. Brand, and the National Natural Science Foundation of China for support of F. Meng and P. Ni (grants
41473039 and 4151101015). We thank M. Lozon (Brock University) for drafting and constructing the figures. We thank the editor, Brendan Murphy, as well as three reviewers (Steve Kesler, Erik Sperling, and an anonymous reviewer), for improving the manuscript into its final form.