Fig. 8: Conceptual model for the biological formation of fossilized As-rich pyrite nuclei.
From: A battle against arsenic toxicity by Earth’s earliest complex life forms
a Oxidized As—arsenate or As5+ (red dots) is released into the ocean by the chemical and oxidative weathering of the continental crust. b During life, As enters the cell, and is detoxified first by reduction to As3+ (c) then extruded by cell membrane transporters or sequestered in intracellular compartments (d). e After death and burial, As is released from intracellular bodies into a localized reduced environment rich in iron (purple dots) where sulfate (green dots) is reduced to sulfides (yellow dots). f Pyrite is formed by microbial sulfate reduction with As acting as a catalyzer of pyrite nucleation. g Arsenic is rapidly consumed in low environmental concentrations. h Pyrite growth led to As depletion away from the core.
