![]() ![]() Starting from the solar nebula to the final accretion, the building material of the Earth underwent a variety of physical and chemical processes that led to the fractionation of elements. Ultimately the material that formed the Earth originated from the solar nebula, which originally had the composition of the Sun. The bulk composition of the Earth is also required to reconstruct the formation of the Earth as a planet and to deduce the different processes that led to its specific chemical composition. The bulk composition of the Earth and that of the distinct terrestrial reservoirs is essential to understand and quantify the major differentiation processes that led to the present-day highly differentiated planet (e.g., McDonough and Sun 1995 Palme and O’Neill 2014). High precision chemical and isotopic analyses in the laboratory of rocky material from inner solar system bodies could complete the knowledge on the chemical, isotopic and mineralogical make-up of the solar nebula just prior to planet formation and enhance our understanding of the evolution of the solar nebula in general and the formation of the rocky planets in particular. Thus, for a complete reconstruction of the conditions that led to the formation of the inner solar system planets (Mercury to Mars) samples from the inner planets Venus and Mercury are of great interest and importance. It is conceivable that Venus and Mercury contain a much larger fraction of this missing component. Variations in nucleosynthetic isotope compositions as well as the strong depletion of moderately and strongly volatile elements points towards a source in the inner solar system for this missing material. ![]() ![]() It is currently not possible to fully define and quantify the different chemical and isotopic materials that formed the Earth, because a major component seems missing in the extant collections of extraterrestrial samples. ![]() In addition, mixing trends of specific isotopes reveal that the Earth is most enriched in \(s\)-process isotopes compared to all other analysed bulk solar system materials. The Earth shows a much stronger depletion of the moderate to highly volatile elements compared to chondrites. However, for some elements there are striking and significant differences. To a first approximation the chemical composition of the bulk Earth bears great similarities to primitive meteorites. Different chondrite classes show distinct chemical and isotopic characteristics, which may reflect heterogeneities in the solar nebula and the slightly different pathways of their formation. Chondritic meteorites are derived from distinct primitive planetary bodies that experienced only limited element fractionation during formation and subsequent differentiation. The chemically most primitive known meteorites are chondrites and they consist mostly of metal and silicates. Thus the rocky planets of the inner solar system are likely the result of the accumulation of numerous smaller primitive as well as differentiated bodies. Gradual increase in the size of solid bodies from dust to aggregates and then to planetesimals finally led to the formation of planets within a few to tens of million years after the start of condensation. Primitive meteorites preserve the chemical and isotopic composition of the first aggregates that formed from dust and gas in the solar nebula during the earliest stages of solar system evolution. ![]()
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