Iridium has no known biological function. Some bacteria and fungi have been shown to leach iridium from igneous rock and meteorites and to accumulate iridium ions from solution. These phenomena are one proposed explanation for the presence of anomalous iridium deposits in some sedimentary rock layers (Dyer et al, 1989).

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Dyer BD, Lyalikova NN, Murray D, Doyle M, Kolesov GM, Krumbein WE. Role for microorganisms in the formation of iridium anomalies. Geology 1989;17:1036-39.