A SEDIMENTARY LI ISOTOPE RECORD THROUGH EARTH'S HISTORY

Lithium (Li) isotopes are an emerging proxy with the ability to track how continental weathering has changed through time. Due to extensive work on Li cycling in modern systems, we now have a sound understanding of the modern Li isotope budget. This modern work has provided a platform for tracking a geologic Li isotope record in order to track global-scale changes in weathering processes and intensity through Earth’s history. In pursuit of this goal, we have generated Li isotope data from marine carbonates, shales, and paleosols from over 60 units, ranging in age from 2.95 Ga to the Modern. Our initial results (which focused on Precambrian paleosols and carbonates), provide evidence for strongly inhibited weathering-mediated clay formation prior to the Paleozoic, which we attribute to the pre-Paleozoic lack of land plants. Standards of sample selection and previous studies of the impact of alteration on the fidelity of Li isotopes indicate that our findings represent a primary, rather than diagenetic trend. Therefore, the long-term Li isotope record provides support for the view that land plants dramatically changed the process of weathering. Li isotopes provide a novel perspective on weathering and the impact on the Earth system of the rise of land plants—one of the most significant transitions in Earth’s history.