16
September 2004
Early solar system: times change
With a half-life of 730,000 years, aluminium-26 decay to magnesium-26 is an ideal chronometer for the early Solar System. A technique known as multi-collector plasma source mass spectrometry has now been used to obtain perhaps the most precise Mg isotope measurements yet. The oldest Solar System materials known are preserved in primitive meteorites as calcium-aluminium refractory inclusions and chondrules. Several reports have suggested that chondrules formed a few million years after refractory inclusions, but this is inconsistent with the expected lifespan of such small particles in the early Solar System. The new method makes it possible to detect excess 26Mg in objects with low Al/Mg ratios, and its use on Allende meteorite material resolves this paradox by showing that calcium-aluminium refractory inclusions and chondrules began to form at the same time; but whereas refractory inclusion formation was over quickly (in 50,000 years), chondrule formation persisted for several million years.
Geochemistry: The clock's second hand
ALEX HALLIDAY
The relative abundances of magnesium isotopes in the Allende meteorite
reveal the precise chronology of the early Solar System — a geochemical
second hand on the clock of creation.
Nature 431, 253–254 (2004); doi:10.1038/431253a
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Mg isotope evidence for contemporaneous formation
of chondrules and refractory inclusions
MARTIN BIZZARRO, JOEL A. BAKER & HENNING HAACK
Nature 431, 275–278 (2004); doi:10.1038/nature02882
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