[meteorite-list] New dating of Allende

From: Pedersen <lbp_at_meteoritecentral.com>
Date: Mon Dec 20 10:25:00 2004
Message-ID: <004d01c4e6a8$10c97970$9f00a8c0_at_star1>

3 scientists from Geological Museum og Danish Lithosf?recenter 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, ?ster Voldgade 10, and
2 Geological Museum, ?ster 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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Received on Mon 20 Dec 2004 10:24:51 AM PST