Abundance variations of refractory elements between different groups of undifferentiated meteorites (chondrites) are within a factor of 2. The elemental abundance pattern of CI chondrites matches that of the solar photosphere reasonably well except for Li, which is depleted in the Sun’s convection zone, and the volatile elements H, C, N, O, and noble gases which are incompletely condensed in chondrites. Macroscopic-scale isotopic heterogeneities are largest for H (D/H varies by 8x) and N (15N/14N varies by 2x). Bulk C- and O-isotopic compositions do not vary by more than a few percent and isotopic heterogeneities are even much smaller for refractory elements. The variations in bulk elemental and isotopic compositions are attributed to variations in the nebula environment from which the chondrites formed. Some meteoritic components (calcium-aluminum-rich inclusions and chondrules) also carry the decay products of now extinct short-lived radioactive nuclides which were either produced locally in the early solar system or in a stellar source shortly before seeding the solar nebula. Large isotopic anomalies with variations over more than four orders of magnitude are observed on a microscopic scale in chondrites. These anomalies are carried by presolar grains that formed mainly in the winds of red giant and asymptotic giant stars and in the ejecta of supernova explosions.

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