Extraterrestrial He in Sediments: From Recorder of Asteroid Collisions to Timekeeper of Global Environmental Changes

Most He in deep-sea sediments is derived from fine-grained extraterrestrial matter known as interplanetary dust particles (IDPs). These particles, typically\50 lm in diameter, are sufficiently small to retain solar windimplanted He with high He/He ratios during atmospheric entry heating. This extraterrestrial He (HeET) is retained in sediments for geologically long durations, having been detected in sedimentary rocks as old as 480 Ma. As a tracer of fine-grained extraterrestrial material, HeET offers unique insights into solar system events associated with increased IDP fluxes, including asteroid break-up events and comet showers. Studies have used HeET to identify IDP flux changes associated with a Miocene asteroid break-up event and a likely comet shower in the Eocene. During much of the Cenozoic, HeET fluxes have remained relatively constant over millionyear timescales, enabling HeET to be used as a constant flux proxy for calculating sedimentary mass accumulation rates and constraining sedimentary age models. We review studies employing HeET-based accumulation rates to estimate the duration of carbonate dissolution events associated with the K/Pg boundary and Paleocene-Eocene Thermal Maximum. Additionally, HeET has been used to quantify sub-orbital variability in fluxes of paleoproductivity proxies and windblown dust. In order to better interpret existing records and guide the application of HeET in novel settings, future work requires constraining the carrier phase(s) of HeET responsible for long-term retention in sediments, better characterizing the He isotopic composition of the terrigenous D. McGee (&) Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA e-mail: [email protected] S. Mukhopadhyay Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA, USA e-mail: [email protected] P. Burnard (ed.), The Noble Gases as Geochemical Tracers, Advances in Isotope Geochemistry, DOI: 10.1007/978-3-642-28836-4_7, Springer-Verlag Berlin Heidelberg 2013 155 end-member, and understanding why observed extraterrestrial He fluxes do not match the predicted variability of IDP accretion rate over orbital timescales.