There are two main processes by which atmospheric carbon dioxide gas can be sequestered into the crustal rocks of the lithosphere. The gas can either be sequestrated as oxidised carbon in the form of lithic carbonate precipitates, which are Arrhenius salts, and so can be formed by geochemical abiotic processes (as well as by biochemical activity) or the gas can be sequestrated as reduced carbon, typically hydrocarbons by biological means. I am assuming that the third process of carbon sequestration, namely polymerisation of methane gas in the presence of radioactive minerals, is not relevant to this discussion, as this requires reduced carbon (methane) for its starting gas and is typically a subterranean process that generates pitchblende (and then graphite by metamorphosis).

The nature and role of stromatolites in the process of atmospheric carbon dioxide sequestration is the issue I would like to focus on. In the published general descriptive literature, there seems to be little acknowledgement that stromatolites are carbonates. The issue of biotic or abiotic origin of the carbonate minerals is irrelevant to the issue of volatile gas to lithic mineral sequestration. If we make the simplistic working assumption that the rate of outgassing of carbon dioxide gas from the mantle is constant throughout Earth’s history, and if we assume an outgassing rate of 1 Earth atmosphere of CO2 per 52 million years (based on an outgassing rate derived from the Venusian atmosphere of 8878 kpa in circa 4.6 billion years), then for the 1.5 billion years of the Archean, some 29 atmospheres of produced CO2 need to be removed for the atmosphere OR the Earth had then lifetime CO2 atmosphere with a surface pressure of circa 40 Atmospheres (including the nitrogen component) and therefore the boiling point of water on Earth 2.5 Bya was some 250 deg C.

The reality probably lies between these two extremes a low C02 atmospheres of say 1 bar (we also require a nitrogen component to allow liquid water to exist), and an upper limit of approx. 40 bar. The key to this analysis is the quantity of carbonates sequestered into the Archean crust by stromatolites. Has anyone got an estimate of the quantity of carbonates produced during the Archean?