[meteorite-list] Re: Any Meteorites of Earth Origin?

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 09:47:11 2004
Message-ID: <200111131754.JAA27404_at_zagami.jpl.nasa.gov>

>>In fact, the impact event that created the Moon
>>probably ejected a lot of material that escaped
>>both the Earth's and Moon's gravity.

>That "ejected material", were it to return to Earth
>now as a meteorite, would be much more like a Lunar
>rock, and nothing at all like a [present] Earth rock.

An Earth rock ejected into space, and then falling back
on Earth as a meteorite would still be very similar
to an Earth rock. Since there is a large variety of
rocks on Earth, I would expect Earth meteorites to
vary as well.

>Dozens of Martian and Lunar meteorites have been
>found.
>Not one terrestrial meteorite has been recognized.

True, but I think the reason they aren't being found
is is that an Earth meteorites would be difficult to
differentiate from Earth rocks, particularly
if the meteorite has lost its fusion crust.

>I find it difficult to accept the notion that
>meteorite hunters worldwide are "missing" them.

I think it is more an issue that there isn't a concerted
effort to find Earth meteorites, and there is no easy
way to identify one from a casual visual inspection.
Let's say a piece of hematite was ejected into space, and
fell back to Earth, and lost its fusion crust due to weathering.
An experienced meteorite collector may find it and pick it up, recognize
it as hematite, and then toss it aside. The tests
that needs to be done to identify it as an Earth meteorite
are done in the laboratory, such as age dating, shock exposure,
cosmic ray exposure, and isotope ratio determination.
The only easy visual clue I can think of for a meteorite hunber
would be the presence of fusion crust.

>But I find it even harder to believe that, among all
>those well preserved Antarctic meteorites that have
>been recovered, not one of them has been identified as
>being anomalous enough to be a potential terrestrial
>meteorite. - ??

You bring up a good point. The meteorites in Antarctic collection
are probably the best candidates for finding an Earth meteorite. I don't
think anyone has made a major effort in identifying potential Earth
meteorites in the Antarctic collection, so they could
be overlooked. Don't forget that the ALH84001 meteorite sat
in the Antarctic collection for 10 years before it was
identified as a Mars meteorite.

Ron Baalke
Received on Tue 13 Nov 2001 12:54:46 PM PST