Steve Willner schrieb:
In article ,
Juergen Barsuhn writes:
http://www.nasa.gov/home/hqnews/2013...Meteorite.html
it is reported that a 2.1 billion years old meteorite
originating from the crust of Mars has been found in the
Sahara. To me, this short report raises more questions than
it answers.

What do you expect from a press release?

A concisely written report on the essential results of the
findings in a form that might be understood by interested
members of the public that finally finance the research work
by their taxes. Most people will never receive an
information that goes beyond of this or similar press releases.

The full paper is at
http://www.sciencemag.org/content/ea...e.1228858.full
but you will need a subscription or pay to read it.

Thank you, but indeed this location is inaccessible for me.
The abstract given lacks any closer information.
I expected this difficukty, so I hoped that somebody out of
this newsgroup might have read the cited paper and would
comment on it.

The authors claim that "their" meteorite is 2.1 billion
years old and hence by far the oldest meteorite from Mars.
As far as I have read, the other meteorites are expected to
be not older than 200 million years. So an age of more than
2 billion yeras would be an extraordinary claim.

........

Martian origin of some meteorites is proven by the oxygen
isotope ratios in small gas bubbles

I think that's only part of the story. In any case, the Martian
orgin of NWA 7034 seems to be based mainly on Fe versus Mn, but there
are lots of other ratios that match Mars. Interestingly, NWA 7034
matches results of Mars rovers and orbiters much better than it
matches SNC meteorites, suggesting that it is more representative of
Mars' current surface than the SNCs are.

I didn't see any mention of gas bubbles, but I might have missed it.

Well - this gas bubble method idea stems from a paper to
which I think Jonathan pointed me about 10 years ago. The
method sounds very complicated experimentally and maybe has
been actually performed only for a (small) part of the
Martian meteorites found in those years in the Antarctica.
Around 2000 thare was a heavy discussion in the internet,
whether these meteorites indeed originate from Mars.


Why should one expect that the isotope ratio in the atmosphere has
remained unchanged through more than 2 billion years?

If the gas bubble method were used for the Sahara-meteorite
...... But maybe other arguments have been used to validitate
its Martian origin.
.......

The data show that the meteorite contains lots of water, hence the
"wet period." Isotope ratios give its age, which I _think_ refers to
the time since the rock solidified. I don't know how that epoch
relates to other studies of Mars' climate, but the name "Amazonian
epoch" does suggest water.

OK. The rock then was formed about 2 billion years ago but
might have left the Martian surface relatively recently due
to an impact event. So this rock had not to overcome a
denser wet atmosphere when leaving the Martian surface, but
only very thin atmosphere of the presence. ?

Regards
Jurgen