Calcium–aluminium-rich inclusion

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Chondrite meteorite with calcium–aluminium-rich inclusions seen as white specks

A calcium–aluminium-rich inclusion or Ca–Al-rich inclusion (CAI) is a submillimeter- to centimeter-sized light-colored calcium- and aluminium-rich inclusion found in carbonaceous chondrite meteorites. They are probably the oldest substances in the Solar System, which formed approximately 4567.30 ± 0.16 Ma.[1]


CAIs consist of minerals that are among the first solids condensed from the cooling protoplanetary disk. They are thought to have formed as fine-grained condensates from a high temperature (>1300 K) gas that existed in the protoplanetary disk at early stages of Solar System formations. Some of them were probably remelted later resulting in distinct coarser textures.[1] The most common and characteristic minerals in CAIs include anorthite, melilite, perovskite, aluminous spinel, hibonite, calcic pyroxene, and forsterite-rich olivine.

Using lead (Pb–Pb) isotopic data determined on CAIs, an age of 4567.30 ± 0.16 million years has been calculated, which can be interpreted as the beginning of the formation of the planetary system.[1] However, due to possible disturbances of the lead isotopic system within the CAIs, this age is possibly only a lower limit of the true age. Radiometric dating with Pb–Pb, Al–Mg and Cr–Mn chronometers shows that the CAIs formed up to 3 million years before the chondrules appeared, although some chondrules formed simultaneously with CAIs.[1][2]

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  1. ^ a b c d Connelly, J. N.; Bizzarro, M.; Krot, A. N.; Nordlund, A.; Wielandt, D.; Ivanova, M. A. (2012). "The Absolute Chronology and Thermal Processing of Solids in the Solar Protoplanetary Disk". Science 338 (6107): 651–655. doi:10.1126/science.1226919. PMID 23118187.  edit
  2. ^ Gilmour, J. (2002). "GEOCHEMISTRY: The Solar System's First Clocks" (PDF). Science 297 (5587): 1658–1659. doi:10.1126/science.1075519. PMID 12215635.  edit