Iron isotope biosignatures: Promise and progress

Isotopic indicators are extremely useful for detecting life in the geologic record. The most notable example is the "C enrichment in organic matter produced by photosynthesis. Compared to both molecular fossils and microfossils, such isotopic indicators are more robust against alteration processes. Mass‐dependent variations in the isotopic compositions of C and other light elements have been studied for half a century. In contrast, little such research had been performed on transition metals until recently because it was difficult to make sufficiently precise isotopic measurements of these elements. Advances in mass spectrometric tools and techniques, especially the development of multiple‐collector plasma source mass spectrometry have simplified such measurements and resulted in rapid progress.