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Nature12 June 2003

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Solar System evolution: Mixed-up meteorites

Chondritic meteorites or chondrites, the oldest rocks in our Solar System, consist of a fine-grained matrix containing chondrules and calcium-aluminium-rich inclusions (CAIs). Chondrules are near-spherical silicate objects about 2 mm in diameter that may once have been molten droplets floating in space. And CAIs are high-melting point materials thought, from lead and aluminium isotope studies, to be formed about 2 million years before the chondrules. On this timetable CAIs would have been the first solids to have formed in the Solar System. But the discovery of a chondrule fragment embedded inside a CAI changes that picture. The opposite case, CAI-bearing chondrules, had been found previously. Now it seems that CAI-forming and chondrule-forming events were not independent, but overlapped during the evolution of the early Solar System.

letters to nature
Contemporaneous formation of chondrules and refractory inclusions in the early Solar System
Nature 423, 728–731 (2003); doi:10.1038/nature01699
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news and views
Meteoritics: A question of timing
Meteorites record the early history of the inner Solar System. A unique object that has been found in one meteorite may add support to a revolutionary idea about how the Solar System formed.
Nature 423, 691–692 (2003); doi:10.1038/423691a
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