Paleontology of Earth's Mantle

Abstract

Solid, liquid, and gaseous products of life's metabolic processes have a profound effect on the chemistry of Earth and its fluid envelopes. Earth's mantle has been modified by the ubiquitous influence of life on recycled lithosphere, with dramatic changes resulting from subduction of redox-sensitive minerals following the rise of photosynthetic oxygen approximately 2.5 billion years ago. Throughout geological time, production and degradation of organic carbon affected minor-element, trace-element, and isotopic systems in the mantle. Carbon in the mantle decreased as carbonate sediments sequestered CO2, but nitrogen concentrations were augmented by subduction of biologically derived ammonium structurally bound in diagenetic minerals. The biologically modulated mantle vents its biosignatures through island arc and oceanic volcanoes, with fractionated sulfur isotopes providing a durable record. Deeply subducted CO2-rich domains are the source of carbonatite melts, as well as eclogitic diamonds with low 13C/12C ratios and remnant biologically derived nitrogen. The mantle preserves a concentrated biological record throughout Earth history, thus giving expectation of finding a Hadean record of life.