THE ARCHEAN PROTEROZOIC TRANSITION The role of serpentinization

THE ARCHEAN PROTEROZOIC TRANSITION The role of serpentinization in the promotion of biogenic activity Prof. W. R. Church

Introductio n n In this talk I will try to explain how oxygen producing biotic activity fed by energy from the olivine - serpentine reaction caused the removal of CH 4 and H 2 S from, and the introduction of oxygen into the Archean atmosphere, eventually leading to the development of ‘greenhouse’ photosynthetic biogenesis during the Lower Proterozoic The talk is a modification of the paper by Melezhik et al. 2005. “Emergence of the aerobic biosphere during the Archean - Proterozoic tranisiton: Challenges of future research”, GSA Today, 15, 11, p. 4 -11. Professor William R. Church

The Archean n n Olivine in the form of komatiite is abundant in the Archean, as is cherty magnetite iron Given the abundance of olivine as a component of the komatiite in the Archean, is it possible that the Archean iron formations are a by-product of the serpentinization process?

Serpentinization as a geochemical energy source for biotic activity n n n The conversion of olivine to serpentine is an exothermic reaction Serpentinization is accompanied by the oxygenic conversion of the fayalite component of olivine to magnetite and silica serpentinites are therefore invariably magnetic. If so, where does the oxygen for the fayalite conversion come from? Could the oxygen be biotic in origin, and could the serpentinization reaction provide the energy for biotic reduction of atmospheric CO 2. Serpentinization of Oceanic Peridotites: Implications for Geochemical Cycles and Biological Activity Gretchen L. Früh. Green, James A. D. Connolly, and Alessio Plas. Geophysical Monograph 144 The sub sea‑floor biosphere at Mid-ocean ridges.

The biotic removal of H 2 S and CH 4 from the atmosphere n n n Details about this topic Supporting information and examples How it relates to your audience

Sulphate reduction and sulphur fractionation in oceanic hydrothermal systems n n Give an example or real life anecdote Sympathize with the audience’s situation if appropriate

The lithologic character of the Lower Prototerozoic n n The Huronian and Medicine Bow Lower Proterozoic successions Aluminosilicates and weathering The location of the first red beds The Gowganda glaciation

Photosynthesis and the Oxyatmoversion event n n Add a strong statement that summarizes how you feel or think about this topic Summarize key points you want your audience to remember

The Lomagundi. Jatuli event n n Summarize any actions required of your audience Summarize any follow up action items required of you

Location map of the Pechenga greenstone belt and the Onega basin

The Shunga Event n n Summarize any actions required of your audience Summarize any follow up action items required of you

Conclusions n n Summarize any actions required of your audience Summarize any follow up action items required of you