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Re: Trivia ?

Walt wrote:

I was just asked a three part question, and wanted to throw it out to the
list before I misspoke. What meteorite has been dated, and by what method,
and, was determined to be the OLDEST on record?


Walt,

That is a tough question to answer with one meteorite name and date.  The
problem is that, as you know, most meteorites are actually a compilation of
various materials which may have different origins and thus different ages.
Similar to cookie dough, the chocolate chips are of different age compared
to the wheat, compared to the other ingredients.

Another problem is which age is being referred to.  Meteorites have several
ages.  They include the terrestrial age (how long it has been sitting on
the earth), cosmic exposure age (how long it was in space after being
broken off the parent body), how long since it was either compiled (as in
chondrites) or melted (achondrites), and how long since the material first
formed as with the birth of our solar system.

Most chondrites have a rough age of 4.6 BA which is the estimated age of
our solar system.  Some achondrites are younger as with the case of most
SNCs.  However, there are a couple of carbonaceous chondrites that may
contain material older than our solar system.  The well known examples of
material this age in the Allende are found in the calcium aluminum
inclusions. These white-to-gray inclusions in the black matrix contain
material suspected to be from the star that went super novae, and
ultimately created the material available for our solar system's current
status.

Another possible exception to the 4.6 BA limit is the Murchison. This
meteorite is suspected to contain interstellar grains.  After several feats
of mathematical gymnastics, it is possible that these grains are 10.6
billion years old making this the oldest known meteorite-except it is not
the meteorite that is that age, but rather some sparsely-spaced grains.

Frank posted some information about this subject a while back.  Here is my
collection of Frank's words.  I have done a little editing, so if there is
a problem with the statements, contact me before assuming an error on
Frank's part.


	We all know of the Murchison carbonaceous chondrite.  Most of us
have it in our collections.  We too, are also aware of amino acids, and
organic compounds found in the meteorite as well. Here is some information
on amino acids in the Murchison meteorite.
1. 	They are believed to be formed by inorganic processes in the early
solar nebulae.
2.	Life on Earth may have had formed by a gentle layering of organic
rich cometary debris. This would provide a means of getting material
through the atmosphere with out destroying by heat. This only one
explanation though, that adequately argues for life forming by
extraterrestrial processes.
3.	There are 79 identified amino acids identified in the Murchison
meteorite.
4.	Data indicate that these were formed by low temperature solutions
with water in the parent body of Murchison.
5. 	And finally, the nature of the amino acids in the Murchison
meteorite is unclear, even after 20 years of research.
	Within the last couple of years, research has shown that the
Murchison meteorite also contains an agglomeration of extra-solar grains.
These grains are of a rare chemical solid called silica carbide (SiC).  It
has been found only in diamond deposits here on Earth. The isotope
composition in these grains does not coincide with the Solar System's, but
does fit well with observed data from stars.
	These grains probably originated from many different types of stars
including: Wolf-Rayet (These stars are hot, and are expelling dust at an
incredible rate, forming planetary nebulae), Carbon burning stars, Novae
(exploding stars), and Supernovae.  The SiC grains are now being used to
determine the age of the Galaxy we inhabit.
	These grains date to about 6 billion years before the origin of the
Solar System. This gives a lower limit on the age of the Milky Way Galaxy
of about 10.5 billion years.  The age of Murchison is still constrained.
	The interstellar grains in Murchison are small. They can barely be
seen with the naked eye.  Typically, they are about .002-10 micrometers in
size. There are four main types: 1) Graphite, 2) Diamond, 3) Silicon
Carbide, 4) Corundum, and one less well known type with Silicon bonded to
Nitrogen. These grains are not abundant in the meteorite. There are only
about five to ten grains per gram. They occur in the black matrix, and are
not collected into inclusions as  the CAI's are.
	What I am about to say is rather profound. It might be, to me at
least, the single most awe-inspiring concept I have ever encountered. The
corundum grains were formed in a supernovae explosion of a star 1.2 times
the size of our Sun. This is determined by Oxygen isotope ratios that
indicate that these grains were derived from a star with a lower metal
content than ours. This reveals that the star must have been at least 1.2
times larger than our sun. The age of the grains is determined by the fact
that a star with 1.2 times the mass of the Sun, "lives" for about 6 billion
years. This indicates the grains were formed at the end of a star's cycle.
Now, to get the age of the Milky Way, take into account the 4.6 billion
year history of our Solar system, and add it to the fact that the grains
formed in the death of a star with a 6 billion year life. You will come up
with a value of 10.6 billion years. They had to form in the outer arm in
which we inhabit, because if they were from another arm of the galaxy, the
distance would be too far to travel in a few million years.


Frank also posted material about the dating of meteorites, but I cannot
find that material at the moment. I will look, but any assistance is
appreciated.

Walt, if you can narrow your question a little, I may be able to get some
more specific information.

Martin
References: