Isotope and trace element geochemistry of Archean chert : Deciphering the ancient oceanic environment and biological activity

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From multidisciplinary geochemical studies using the fresh drillcore samples of 3.46 Ga chert and 3.2 Ga chert/BIF/black shales, the following exciting results are obtained. Ferrous iron from hydrothermal venting was oxidized, most likely by dissolved oxygen, in the 3.46 Ga deep hot ocean that was influenced by hydrothermal activity. In the 3.2 Ga ocean, that was shown from our studies to have been very similar to the 3.46 Ga ocean, microbial denitrification, oxygenic photosynthesis, and sulfate reduction were all active. Our major conclusion is that the Mesoarchean ocean was generally oxic with local and temporal existence of anoxic water bodies. This study has far-reaching implications for the early co-evolution of microbial biosphere and surface environments of the Earth.