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Register a new userChemically defining the building blocks of the Earth
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Chondrites are undifferentiated sediments of material left over from the earliest solar system and are widely considered as representatives of the unprocessed building blocks of the terrestrial planets. The chondrites, along with processed igneous meteorites, have been divided into two broad categories based upon their isotopic signatures; these have been termed the CC and NC groups and have been interpreted as reflecting their distinctive birth places within the solar system. The isotopic distinctiveness of NC and CC meteorites document limited radial-mixing in the accretionary disk. The enstatite and ordinary chondrites are NC-type and likely represent samples from inner solar system (likely $<$4 AU). Measurement and modeling of ratios of refractory lithophile elements (RLE) in enstatite chondrites establish these meteorites as the closest starting materials for the bulk of the silicate Earth and the core. Comparing chondritic and terrestrial RLE ratios demonstrate that the Bulk Silicate Earth, not the core, host the Earths inventory of Ti, Zr, Nb, and Ta, but not the full complement of V.
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Geochemical and astronomical evidence demonstrate that planet formation occurred in two spatially and temporally separated reservoirs. The origin of this dichotomy is unknown. We use numerical models to investigate how the evolution of the solar protoplanetary disk influenced the timing of protoplanet formation and their internal evolution. Migration of the water snow line can generate two distinct bursts of planetesimal formation that sample different source regions. These reservoirs evolve in divergent geophysical modes and develop distinct volatile contents, consistent with constraints from accretion chronology, thermo-chemistry, and the mass divergence of inner and outer Solar System. Our simulations suggest that the compositional fractionation and isotopic dichotomy of the Solar System was initiated by the interplay between disk dynamics, heterogeneous accretion, and internal evolution of forming protoplanets.
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The most abundant components of primitive meteorites (chondrites) are millimeter-sized glassy spherical chondrules formed by transient melting events in the solar protoplanetary disk. Using Pb-Pb dates of 22 individual chondrules, we show that primary production of chondrules in the early solar system was restricted to the first million years after formation of the Sun and that these existing chondrules were recycled for the remaining lifetime of the protoplanetary disk. This is consistent with a primary chondrule formation episode during the early high-mass accretion phase of the protoplanetary disk that transitions into a longer period of chondrule reworking. An abundance of chondrules at early times provides the precursor material required to drive the efficient and rapid formation of planetary objects via chondrule accretion.
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