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Small isotopic differences in the atomic abundance of neodymium-142 (142Nd) in silicate rocks represent the time-averaged effect of decay of formerly live samarium-146 (146Sm) and provide constraints on the timescales and mechanisms by which planetary mantles first differentiated. This chronology, however, assumes that the composition of the total planet is identical to that of primitive undifferentiated meteorites called chondrites. The difference in the 142Nd/144Nd ratio between chondrites and terrestrial samples may therefore indicate very early isolation (<30 Myr from the formation of the Solar System) of the upper mantle or a slightly non-chondritic bulk Earth composition. Here we present high-precision 142Nd data for 16 martian meteorites and show that Mars also has a non-chondritic composition. Meteorites belonging to the shergottite subgroup define a planetary isochron yielding an age of differentiation of 40 ± 18 Myr for the martian mantle. This isochron does not pass through the chondritic reference value (100 × ε142Nd = -21 ± 3; 147Sm/144Nd = 0.1966). The Earth, Moon and Mars all seem to have accreted in a portion of the inner Solar System with ∼5 per cent higher Sm/Nd ratios than material accreted in the asteroid belt. Such chemical heterogeneities may have arisen from sorting of nebular solids or from impact erosion of crustal reservoirs in planetary precursors. The 143Nd composition of the primitive mantle so defined by 142Nd is strikingly similar to the putative endmember component ‘FOZO’ characterized by high 3He/4He ratios. [ABSTRACT FROM AUTHOR]

The discovery in primitive components of meteorites of large oxygen isotopic variations that could not be attributed to mass-dependent fractionation effects has raised a fundamental question: what is the composition of the protosolar gas from which the host grains formed? This composition is probably preserved in the outer layers of the Sun, but the resolution of astronomical spectroscopic measurements is still too poor to be useful for comparison with planetary material. Here we report a precise determination of the oxygen isotopic composition of the solar wind from particles implanted in the outer hundreds of nanometres of metallic grains in the lunar regolith. These layers of the grains are enriched in16O by>20±4‰relative to the Earth, Mars and bulk meteorites, which implies the existence in the solar accretion disk of reactions-as yet unknown-that were able to change the17O/16O and18O/16O ratios in a way that was not dependent strictly on the mass of the isotope. Photochemical self-shielding of the CO gas irradiated by ultraviolet light may be one of these key processes, because it depends on the abundance of the isotopes, rather than their masses. [ABSTRACT FROM AUTHOR]

Interstellar silicon carbide grains in meteorites provide a novel means for studying the carbon-star population of about 5 x 10 9 years ago. Their 12C/13C ratios differ greatly from the solar value but resemble those of present-day carbon stars, implying little change in galactic 13C inventory. Isotope data on nitrogen and silicon suggest that the silicon carbide grains come mainly from red giants, with small contributions from novae. [ABSTRACT FROM AUTHOR]

Compares published hafnium (Hf)-neodymium (Nd) isotope data on supracrustals from Isua, Greenland, with similar data on lunar rocks and the SNC (martian) meteorites. Evidence that the geochemical signature of the Archaean mantle was partly inherited from the initial differentiation of the Earth; Remnants from an early layering in the modern deep mantle.

This article informs that the existence or radioactive aluminium and other short-lived nuclides in the early solar system suggests a source of heat for melting planetesimals, and provides a way of deducing time differences between events. It also means that some stellar process must have created significant amounts of aluminium just before the solar system formed. It is further informed that of the objects found inside chondrites, two have particular significance in the early history of the solar system: calcium aluminium refractory inclusions (CAIs) and chondrules. CAIs are the earliest object yet identified that bear clear isotopic evidence of having formed inside the solar system.

Investigates the birth of the Solar System. Experiments on the selection of meteorites; Calculation of core-formation ages based on isotope data; Assumption that millimeter-sized particles of calcium and aluminum silicates found inside some meteorites are the oldest objects in the Solar System.