in
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.
As i had learned from the moderators of this group, the
Martian origin of some meteorites is proven by the oxygen
isotope ratios in small gas bubbles contained in the
meteorite amd that agrees with the isotope ratio found in
the Martian atmosphere by the two Viking landers in 1976.
(There are apparently no more recent measurements of these
isotope ratios, maybe Curiosyity will provide new results.)
However, if the age of the meteorite is correct: Why should
one expect that the isotope ratio in the atmosphere has
remained unchanged through more than 2 billion years?
Especially, if it is claimed that the meteorite left the
Martian crust during a wet period of Mars?

Most Martian meteorites appear to have been molten,
indicating a volcanic origin. As there had been volcanoes on
Mars, but e.g. not on the Moon in the last several billion
years, there is an additional argument for the Martian
origin of these meteorites. But the recently identified
meteorite is expected to come from the Martian crust.
Whereas volcanoes might be able to reach the Martian escape
velocity for parts of their ejecta, it is hard to imagine
that a grazingly incident meteorite might throw parts of the
crust into space, especially if one thinks of a maybe dense
wet atmosphere breaking the incoming meteorite and the
throen out crust material.

Presently I have no access to the paper announced in that
short communication, maybe other readers can shed some light
on this topic.

All the best
Jurgen