[meteorite-list] New dating of Allende

[Pedersen]

3 scientists from Geological Museum og Danish Lithosfærecenter at Geocenter 
Copenhagen in Denmark,  has made the best dating of material from the birth 
of the solarsystem, so far.

4.567,2 million years old, the Allende meteorite is the oldest know matter 
from the solar system. 30 million years older than the earth, and 700 
million years older than the oldest rock known on Earth.

Best wishes
Lars Pedersen


Abstract from Nature 431, 275 - 278 (16 September 2004); 
doi:10.1038/nature02882

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Mg isotope evidence for contemporaneous formation of chondrules and 
refractory inclusions
MARTIN BIZZARRO1,2, JOEL A. BAKER1,3 & HENNING HAACK2
1 Danish Lithosphere Centre, Øster Voldgade 10, and
2 Geological Museum, Øster Voldgade 5-7, DK-1350, Denmark
3 School of Earth Sciences, Victoria University of Wellington, PO Box 600, 
Wellington, New Zealand

Correspondence and requests for materials should be addressed to M.B. 
(mbi at dlc.ku.dk).


Primitive or undifferentiated meteorites (chondrites) date back to the 
origin of the Solar System, and thus preserve a record of the physical and 
chemical processes that occurred during the earliest evolution of the 
accretion disk surrounding the young Sun. The oldest Solar System materials 
present within these meteorites are millimetre- to centimetre-sized 
calcium-aluminium-rich inclusions (CAIs) and ferromagnesian silicate 
spherules (chondrules), which probably originated by thermal processing of 
pre-existing nebula solids. Chondrules are currently believed to have formed 
2-3 million years (Myr) after CAIs (refs 5-10)-a timescale inconsistent with 
the dynamical lifespan of small particles in the early Solar System. Here, 
we report the presence of excess 26Mg resulting from in situ decay of the 
short-lived 26Al nuclide in CAIs and chondrules from the Allende meteorite. 
Six CAIs define an isochron corresponding to an initial 26Al/27Al ratio of 
(5.25  0.10)  10-5, and individual model ages with uncertainties as low as 
30,000 years, suggesting that these objects possibly formed over a period as 
short as 50,000 years. In contrast, the chondrules record a range of initial 
26Al/27Al ratios from (5.66  0.80) to (1.36  0.52)  10-5, indicating that 
Allende chondrule formation began contemporaneously with the formation of 
CAIs, and continued for at least 1.4 Myr. Chondrule formation processes 
recorded by Allende and other chondrites may have persisted for at least 2-3 
Myr in the young Solar System.

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