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 Universität Berlin, the other half is still on the meteorite. Let’s hope it recovers. Cheers Svend "Meteorite-Recon.com" <i...@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 Universität Berlin, the other half > is > still on the meteorite. Let’s hope it recovers. > > Cheers > > Svend > > > MEM <mstrema...@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 <mich...@rocksfromspace.org> > > > To: meteorite-list@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 > > ______________________________________________ > > Visit the Archives at > > http://www.meteoritecentral.com/mailing-list-archives.html > > Meteorite-list mailing list > > Meteorite-list@meteoritecentral.com > > http://six.pairlist.net/mailman/listinfo/meteorite-list ______________________________________________ Visit the Archives at http://www.meteoritecentral.com/mailing-list-archives.html Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list