[meteorite-list] Rocks from Space Picture of Day - January 5, 2011

From: Meteorite-Recon.com <info_at_meteoritecentral.com>
Date: Wed, 5 Jan 2011 18:29:02 +0100 (CET)
Message-ID: <2096711352.341896.1294248542149.JavaMail.open-xchange_at_oxltgw00.schlund.de>

It?s interesting that you mention it Elton. We actually looked into that.
Although the meteorite shows zero visible oxidation, its quite possible the fall
event dates back more than two decades. In case no short living cosmogenic
radionuclides, 22Na in particular, can be detected, our idea was to have the age
of the lichen determined (which could be several decades) in order to derive at
least a minimum terrestrial age for the meteorite.
?
This appears to be difficult though. While lichonometric age determination is
well established and works for crustose lichen, it can not be applied to
frucitose lichen.
?
Radionuclide measurement might be a probable way. But as we had to discover,
isotopic age determination of lichens is quite a tricky subject. Contrary to the
process in wood or bones, where the isotopes are fixed in the structure, the
lichen thalli are composed of fungi-hyphes which die off and are replaced
periodically during the life cycle of the lichen.
?
However, there are certain crystalline sediments within the thallus (e.g.
oxalates) which may stay and remain on the lichen and thus preserve the isotopes
collected over the life time of the plant. Our specimen fortunately appears to
have aggregated quite some oxalates, so that?s the way we are currently
following.
?
There are only very few works on isotopic age dating of frucitose lichen. Most
papers are dealing with C-isotopes. Uranium-isotopes in lichens are mostly
measured to determine air pollution only, and there is no data for our find
location which correlates them with age. So 238U und 232Th are of no use. Trying
to detect 14C in the oxalates currently appears the most promising approach.

I am absolutely no expert, neither in lichens nor in isotopic age dating, so I?d
appreciate any corrections or additional thoughts.
?
To answer Matthias? question: of course we were interested to preserve the main
body of the lichen ?in situ? after sampling it, but I must admit it doesn?t look
too healthy now. It didn?t take the removal of a sample from its habitat by
means of an alcohol-cooled wire saw too well. Besides, its natural climatic
environment is hard to simulate. A part of?the plantlet?is now archived in the
herbarium of the Botanical Museum of Freie Universit?t Berlin, the other half is
still on the meteorite. Let?s hope it recovers.
?
Cheers
?
Svend



"Meteorite-Recon.com" <info at niger-meteorite-recon.de> hat am 5. Januar 2011 um
18:28 geschrieben:

>
> It?s interesting that you mention it Elton. We actually looked into that.
> Although the meteorite shows zero visible oxidation, its quite possible the
> fall
> event dates back more than two decades. In case no short living cosmogenic
> radionuclides, 22Na in particular, can be detected, our idea was to have the
> age
> of the lichen determined (which could be several decades) in order to derive
> at
> least a minimum terrestrial age for the meteorite.
> ?
> This appears to be difficult though. While lichonometric age determination is
> well established and works for crustose lichen, it can not be applied to
> frucitose lichen.
> ?
> Radionuclide measurement might be a probable way. But as we had to discover,
> isotopic age determination of lichens is quite a tricky subject. Contrary to
> the
> process in wood or bones, where the isotopes are fixed in the structure, the
> lichen thalli are composed of fungi-hyphes which die off and are replaced
> periodically during the life cycle of the lichen.
> ?
> However, there are certain crystalline sediments within the thallus (e.g.
> oxalates) which may stay and remain on the lichen and thus preserve the
> isotopes
> collected over the life time of the plant. Our specimen fortunately appears to
> have aggregated quite some oxalates, so that?s the way we are currently
> following.
> ?
> There are only very few works on isotopic age dating of frucitose lichen. Most
> papers are dealing with C-isotopes. Uranium-isotopes in lichens are mostly
> measured to determine air pollution only, and there is no data for our find
> location which correlates them with age. So 238U und 232Th are of no use.
> Trying
> to detect 14C in the oxalates currently appears the most promising approach.
>
> I am absolutely no expert, neither in lichens nor in isotopic age dating, so
> I?d
> appreciate any corrections or additional thoughts.
> ?
> To answer Matthias? question: of course we were interested to preserve the
> main
> body of the lichen ?in situ? after sampling it, but I must admit it doesn?t
> look
> too healthy now. It didn?t take the removal of a sample from its habitat by
> means of an alcohol-cooled wire saw too well. Besides, its natural climatic
> environment is hard to simulate. A part of?the plantlet?is now archived in the
> herbarium of the Botanical Museum of Freie Universit?t Berlin, the other half
> is
> still on the meteorite. Let?s hope it recovers.
> ?
> Cheers
> ?
> Svend
>
>
> MEM <mstreman53 at yahoo.com> hat am 5. Januar 2011 um 16:46 geschrieben:
>
> > I know that lichen growth-rates have been used to estimate the age of some
> > geological events.? In this case, the radionuclide derived age might be used
> > to
> > verify growth rates for the this species of lichen in this environment.? It
> > would be interesting to compare the two derived ages for consistency.
> >
> > Another, "who would have thought such a thing could exist" photo of the
> > day.?
> > ?
> > Thanks Mike and congrats? Svend et al.
> >
> > Elton
> >
> >
> >
> > ----- Original Message ----
> > > From: Michael Johnson <michael at rocksfromspace.org>
> > > To: meteorite-list at meteoritecentral.com
> > > Sent: Wed, January 5, 2011 9:26:06 AM
> > > Subject: [meteorite-list] Rocks from Space Picture of Day - January 5,
> > > 2011
> > >
> > > http://www.rocksfromspace.org/January_5_2011.html
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Received on Wed 05 Jan 2011 12:29:02 PM PST