Whoops that should have read non-irons swept clean in 100 million years not 100 thousand years.
-- Eric Olson ELKK Meteorites http://www.star-bits.com > <If all ungrouped iron meteorites are derived from the cores of differentiated > bodies, the question is: > where is all the crust gone? Why don't we have many more (at least 92) different > types of achondrites in our meteorite collections?> > > >From Mittlefehldt et al, chapter 4 p4-15 "Planetary Materials" Reviews in > Mineralogy Vol 36 > > "cosmic ray exposure ages of iron meteorites are typically in the range of 200 > to 1000 Ma, some 5 to 50 times longer than typical for stony meteorites. Tight > clusters in exposure ages for groups IIIAB and IVA suggest discrete breakup > events for their parent bodies 650 +/- 75 and 420 +/- 70 Ma ago, respectively > (Voshage and Feldmann 1979). No other clusters have been observed. The highest > 41K/40K exposure age measured for an iron meteorite is 2.3 Ga, or half the age > of the solar system, for the ungrouped Deep Springs iron." > > The longest CRE exposure age I know of for a non-iron is Soko-Banja at 71.1 > Ma although there may be others I don't know of. This does exclude lunars > which do have CRE ages of up to a billion years. > So if the non-irons are swept clean in 100,000 years or less and the irons > hang around for a up to a billion or more that would explain why we see more > variety in iron parent bodies. > > -- > Eric Olson > ELKK Meteorites > http://www.star-bits.com > > > > ______________________________________________ > Meteorite-list mailing list > [EMAIL PROTECTED] > http://six.pairlist.net/mailman/listinfo/meteorite-list ______________________________________________ Meteorite-list mailing list [EMAIL PROTECTED] http://six.pairlist.net/mailman/listinfo/meteorite-list
