PALEOMINERALOGY OF THE HADEAN EON: A PRELIMINARY SPECIES LIST

The Hadean Eon, encompassing Earth's first 550 million years, was a time of significant planetary evolution. Nevertheless, prebiotic Earth's near-surface environment may have held no more than approximately 420 different rock-forming or accessory mineral species that were widely distributed and/or volumetrically significant. This relative Hadean mineralogical parsimony is a consequence of the limited modes of mineral paragenesis prior to 4 Ga compared to the last 3.0 billion years. Dominant Hadean Eon mineralizing processes include the evolution of a diverse suite of intrusive and extrusive igneous lithologies; hydrothermal alteration over a wide temperature range, notably serpentinization; authigenesis in marine sediments; diagenesis and low-grade metamorphism in near-surface environments; and impact-related processes, including shock mineralization, creation of marginal hydrothermal zones, and excavation of deep metamorphosed terrains. On the other hand, the Hadean Eon may have been notably lacking in mineralization generated by plate tectonic processes, such as subduction zone volcanism and associated fluid-rock interactions, which result in massive sulfide deposition; convergent boundary orogenesis and consequent extensive granitoid-rooted continental landmasses; and the selection and concentration of incompatible elements in complex pegmatites, with hundreds of accompanying minerals. The dramatic mineralogical consequences of life are reflected in the absence of Hadean biomineralization; for example, the lack of extensive carbonate deposits and the associated restricted development of skarn and cave minerals prior to 4 Ga. Most importantly, it was not until after the establishment via photosynthesis of significant near-surface redox gradients that supergene alteration, redox-controlled ore deposition, and subaerial weathering in an oxidizing environment could diversify Earth's near-surface mineralogy. These post-Hadean processes may be responsible for over 4000 of the more than 4800 approved mineral species. Any scenario for life's origins that invokes minerals as agents of molecular synthesis, selection, protection, or organization must take into account the limited mineralogical repertoire of the time.