[meteorite-list] Suche nach den ältesten Gesteinen im Sonnensystem (in German and now also in English :-)

From: bernd.pauli_at_paulinet.de <bernd.pauli_at_meteoritecentral.com>
Date: Mon Feb 6 15:47:48 2006
Message-ID: <DIIE.0000002400004395_at_paulinet.de>

Peter wrote:

Hello All (especially the German speaking part!),

http://idw-online.de/pages/de/news146006


Translation provided by Bernd Pauli ;-)


Looking for the Oldest Rocks in our Solar System

The German Research (DFG) Consortium has granted the Universities of Cologne and
Bonn 1.2 million Euros to enable them to purchase a high-precision mass spectrometer.
This instrument will help the mineralogists search for the oldest matter in the solar
system. They also intend to examine closely lunar rocks in a new joint lab for isotope
chemistry.

14.7 mio. years ago green glass hailed from the sky over what is now the Czech Republic.
Shortly before a huge meteorite had struck in Southern Germany creating a crater 23 km
in diameter: The N?rdlinger Ries (the Ries Crater).

The projectile was vaporized and along with it several km^3 of earth rock. Within a few minutes
a cloud developed and rose up to a height of over 100 km. It was from that cloud that the glassy
bodies condensed that hereafter were to rain down south of where Prague is now situated.

These moldavite vary in size from 1 to 10 cm. They resemble broken beer bottles (!) and obviously
have little in common with the rocks we nowadays find hundreds of kilometers farther west in the
Ries Crater Basin.

"But isotopic measurements showed that moldavites really come from the impact of a meteorite",
says Bonn mineralogist Prof. Dr. Carsten M?nker.

M?nker's team of scientists and his colleague from Cologne, Dr. Herbert Palme, have just recently
been granted a new measuring instrument that may prove this theory with even higher precision:

An ultra-high-precision mass spectrometer that allows scientists to measure the amount of different
isotopes in rocks and minerals. "Isotopes are particles of one and the same chemical element, which,
however, have different masses, in other words, whose weight differs", says M?nker.

The new instrument will enable us to measure the presence of a certain isotope in a solid body to
a precision of 0.001 percent.

With this new instrument, which cost 1.2 million Euros, the mineralogists now intend to search for
the oldest rocks and minerals in the solar system. According to the Cologne-Bonn mineralogists,
recent research results show the record-holders are the so-called iron meteorites. They are as old
as 4.570 billion years and thus formed about 3 mio. years before the oldest material dated in the
solar system.

Isotopes serve as "clocks" to the mineralogists: many isotopes are not stable but decay over the
course of time. One gram of uranium will only leave a little more than have as much a 4.5 billion
years, the other half gram has been transformed to lead.

Measuring the proportion of uranium to lead in very ancient terrestrial rocks, one can deduce the
approximate minimum age of our Planet Earth - albeit only rather vaguely as the Earth constantly
rejuvenates its surface layers through tectonic movements.

"But there are also elements with such a short half-life that they had completely decayed after a few
100 million years after the formation of the Earth", says M?nker. "They allow much more precise dating
of the age of our planet provided you have a mass spectrometer that is sensitive enough for such
measurements."

An example: the isotope 182-hafnium is extinct. It transforms into 182-wolfram with a half-life of nine
million years - wolfram (tungsten) is the metal electric-lamp filaments are made of. When the Earth
started cooling shortly after its formation, most of the metallic tungsten sank to the metallic core
of the Earth. But as there was still some hafnium-182 in the crust of our planet that had by that time
already solidified, some tungsten was still formed there.

Measuring the amount of tungsten-182 in terrestrial rocks, allows scientists to compute the formation
age of the metallic core of the Earth - a much more reliable value of the age of our planet (about 4.53
billion years).

"But, as a reference value, we need cosmic material, for example, from a meteorite that fell to Earth",
explains M?nker. "Only then can we establish a value of the amount of tungsten we would have on Earth
today if the major part of it had not settled to the core of the Earth."

That's why the Bonn-Cologne team of mineralogists specializes in the research of extraterrestrial
samples. Fortunately there is plenty of it. About 20,000 meteorites with a mass of more than 100
grams reach the Earth's surface every year. It's particularly easy (!) to find them at the poles or in
Hot Deserts like the Sahara Desert: on the one hand, rocks there weather more slowly, and, on the
other hand, they are more easily recognizable due to the dark, contrasting color of their crusts.

"But we also do research on lunar rocks that have been brought back from the Apollo missions",
M?nker says. The astronauts had collected about 360 kg and the material is extremely precious
so that you can only use up minute quantities for research. No problem for the new instrument",
states Prof. M?nker. "The spectrometer is so sensitive that we can measure the isotopes in
extremely minute samples".

To: p.marmet_at_mysunrise.ch
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Received on Mon 06 Feb 2006 03:47:46 PM PST