AW: [meteorite-list] Lunar/Martian controversy

From: Norbert Classen <trifid_at_meteoritecentral.com>
Date: Thu Apr 22 10:18:02 2004
Message-ID: <NCBBKMGDKLMGIBALJOFCCEHJDPAA.trifid_at_timewarp.de>

Hi Mark, John, and List,

Since Eric already addressed an error in the first answer regarding
the absolute ages of Martian, and lunar meteorites, let me address an
error in the second answer:

> Q: How long have these planetary meteorites been on earth?
> A: Probably all less than 25,000 years. So we know the rate of finds
> from material found that probably fell in recent times. 1 to 1

Humm, this isn't true, at least not for several lunar meteorites
in our collections. More recent studies show that some lunaites
exhibit remarkably long terrestrial residence ages. For example,
the terrestrial age for the lunar breccia Dhofar 025 (and pairings,
e.g., Dho 301, 304, and 308) is estimated at 500ka (yes, that's
500,000 or half-a-million years!). Some Antarctic finds are also
much, much older than 25ka, such as MAC 88104/88105 that shows a
terrestrial age of about 200ka. In fact, most lunaites have
terrestrial ages of 10ka (10,000 years) or more, and only a few
are thought to have fallen in more or less recent times.

I'm not sure regarding the Martian meteorites of which at least
four represent witnessed falls - a fact that raises even more
questions...

All the best,
Norbert
Received on Sat 20 Dec 2003 01:13:33 PM PST