b'14 Carnegie Science|Fall 2020Coauthors Elizabeth Cottrell (left) and Marion Le Voyer (middle) are both former Carnegie postdoctoral fellows. They are now with the Smithsonian Institution. They worked with the late staff scientist Erik Hauri (right) on this research. Images courtesy Jennifer Renteria, Smithsonian, and the Carnegie Institution for ScienceCarbon Hidden in Earths Core During Formative YearsC arbon is essential for life, is vital to our planetsMid-AtlanticRidgegeologic processes, and has an important impact on the atmosphere and oceans. However, the total South Americaamount of carbon on Earth remains a mystery,Spinbecause much is inaccessible in the deep planet.transition AfricaNew work published in the Proceedings of the NationalzoneAcademy of Sciences reveals how carbon behaved during Earths violent formative period. The findings can help scientists understand how much carbon exists in the planets core and the contributions it could make to the chemical and dynamic activity thereincluding the convection that powersLower Dthe magnetic field, which protects Earth from cosmic radiation.mantle OuterThe group was comprised of Harvard Universitys Rebeccacore InnerFischer, the Smithsonian Institutions Elizabeth Cottrell andcoreThis artwork shows Earths dynamic interior. The lowest layer, the core, is comprised Marion Le Voyer, both former Carnegie postdoctoral fellows,mostly of iron and nickel. But the density suggests lighter elements too, such as carbon, Yale Universitys Kanani Lee, and Carnegies late Erik Hauri, thesilicon, oxygen, sulfur, or hydrogen. To research these inaccessible depths, researchers memory of whom the authors acknowledged.conduct high-pressure and higher-temperature experiments in the lab to quantify the cores composition. Earths core is comprised mostly of iron and nickel. But itsImage courtesy Sergey Lobanov, Carnegie Institution for Sciencedensity indicates other lighter elements as well, such as carbon, silicon, oxygen, sulfur, or hydrogen. Its been long suspected thatcompatibility with the iron comprising the core while under the theres a tremendous reservoir of carbon hiding there. But toextreme pressures and temperatures found in the deep Earth quantify it, the team had to use laboratory mimicry. during its formation. To understand present-day Earths carbon content, weWe found that more carbon would have stayed in the went back to our planets babyhood, when it accreted frommantle than we previously suspected, explained Cottrell. This material surrounding the young Sun and eventually separatedmeans the core must contain significant amounts of other into chemically distinct layerscore, mantle, and crust, saidlighter elements, such as silicon or oxygen, both of which Fischer. We set out to determine how much carbon entered thebecome more attracted to iron at high temperatures.core during these processes. Despite this surprising discovery, the majority of Earths They conducted lab experiments that compared carbonstotal carbon inventory does likely exist down in the core. But it compatibility with the silicates comprising the mantle to itsstill makes up only a negligible component of the cores overall composition. Overall, this important work improves our understanding of The teams experiments comparedhow Earths carbon was accumulated during the planetary carbons compatibility with the silicatesformation process and sequestered into the mantle and core as that comprise the Earths mantle (outer circle) to its compatibility with the ironthey chemically differentiated, that comprises the planets core (innerconcluded Richard Carlson, director ofSUPPORT:circle) while under conditionsCarnegies Earth and Planets Laboratory,A National Science Foundation mimicking the Earths interior during itspostdoctoral fellowship formation. They found that morewhere Hauri worked. I only wish Eriksupported this work, which was carbon would have stayed in thewas still with us to see the resultsperformed, in part, under the mantle than previously thought.auspices of the Department of Image courtesy Rebecca Fischer, Elizabethpublished. Energy by Lawrence Livermore Cottrell and Marion Le Voyer, Kanani Lee, andNational Laboratory.the late Erik Hauri'