Hi, E and List,
Bret Gladman's simulations of rocks blasted off
the Earth by impact show about 50% of them being
"re-captured" from independent orbits and returning
as "meteorites." The time scale for re-capture varies
from 10,000 years to 10,000,000 years. So, if there
were any returns from the Ries impactor, they would
already be here, mostly likely.
Sedimentary meteorites are discussed here:
http://meteorite-identification.com/mwnews/BLECKENSTAD.htm
Monica Grady, looking for a possible Martian
sedimentary stone, wrote a paper requesting
museums and collections to look for such anomalous
stones as might be found in their dusty drawers or
cabinets in this publication (p. 77):
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19960027473_1996032004.pdf
Sterling K. Webb
-------------------------------------------------------------
----- Original Message -----
From: "Mr EMan" <[email protected]>
To: "meteoritelist" <[email protected]>
Sent: Friday, June 05, 2009 10:58 PM
Subject: Re: [meteorite-list] A question????? another answer
You are too kind, Carl. Let me address your questions inside your
quote:
--- On Fri, 6/5/09, [email protected] <[email protected]> wrote:
Q: I have a few follow-up questions for you; If an Earth meteorite
(terrene) were to return back to Earth, would we be able to identify
it correctly?
A: Yes and No. IF you look at the locations of recent major
impacts(80 Million years or later) and consider the bedrock/ target
rock-type at the launch origin. It narrows the filed of possible rock
types.
The best candidate is Reis crater in Germany which lies on limestone.
The Canadian shield cluster and Popogui impacts are far too (old we
think) and that leaves Chesapeake, Chicxulub, The un-named crater in
the North Sea off Scotland and Wetumpka Al. So far as I know all
these excavated down to deep crystalline basement rock so most have a
component of igneous rock mixed with the sedimentary kinds.
Statistically the older the impact the more likely that any orbitally
ejected material will have already fallen back long before mankind
existed. Someone somewhere did a study of the physics on what sized
crater had enough energy to eject material at escape velocity and
seems like it was in the range of 5 miles/8km someone with a better
database might chime in.
Chicxulub target rocks included slates,sandstone, sulfate rocks and
weathered lavas . The sulfates are generally too fragile. Sandstone
has a wide range of hardness and is more difficult to predict launch
integrity and space survival. Quartzite remains the best candidate for
launch, survival and recognition but Popagui in Siberia is over 200
myo(?)(Geoff Notkin knows, he fed the mosquitoes there one summer).
The crystalline bedrocks are usually pyroxene, mica, feldspar, and
silica(quartz) mixtures. Earth rocks tend to have larger grain and
clast sizes. Certain grain sizes could only come from Earth as no
other planet other than Venus could grow them.
That leaves a granitoid rocks and quartzite for best chance of
survival and recognition. A fusion crust on those: granite --white to
brown with specs of black. Quartzite probably a frosty clear glass
coating.
When Limestone is heated it does not melt but turns into highly
soluble lime (CaO) and Carbon dioxide ( CO2)...so there isn't a fusion
crust. It would be white until the first rain.
Q: That is to say would we not simply ASSume it came from the moon? As
a
moon meteorite would also have Earth air or isotopes?
A: Owing that the Earth and Moon came from the same stock we share the
same isotope abundances so there is no isotope ratio test to
differentiate them. Again grain size and clast sizes would be larger
on material from Earth
We make new supposed Lunar meteorite discoveries with new
materials all the time. So again I ask is there a way to be
certain where it came from? I ask because if is not mostly
plagioclase, it seems to me most investigators would simply
toss it aside and say; it is not a meteorite, that is a rind
or weathered Earth rock not fusion crust.
Yes there is so much industrial slag about even regular moon
meteorites look like it but I will keep looking for out of place
rocks. Moon material from the Mares is hard to differentiate from
earth basalt save for the clasts. The feldspars could come from
anywhere in New Hampshire, Vermont-- actually most all of New England,
so again anyone looking would need a very trained eye. I think the
first identified Earthite will be the one that crashes through a roof
and makes someone take a hard look.
Right now unless it were very very old due to an extremely large orbit
that took 700-1300 million years to decay-- there are no candidate
craters on Earth that are in feldspar-rich bedrock that come to mind.
Actually Nininger(?) or someone--found a limestone object that was
reported to be a fall and in fact he thought it to be a meteorite but
it was so unlike anything known it was unable to prove it. The
where-a-bouts of the object is unknown. It is listed as a
psuedo-meteorite in the Natural History (British) Museum's Catalog of
meteorites
Q: So, another
question would be this; if it clearly has a fusion crust
complete with the gas bubbles would there be a way to prove
it is in fact a genuine fusion crust???
The short answer: Cosmic ray tracks and enriched tritium from solar
wind would be proof that the material had been in space. Fusion crust
in my book is over rated as "proof" owing to the wide occurrence of
industrial glass so widely spread on Earth AND poorly
understood/recognized accurately as everyone claims fusion crust when
in fact the crust is long gone and they are looking at the ablation
surface. An ablation surface can look like water or wind-worn
surfaces.
You are Welcome, Elton
______________________________________________
http://www.meteoritecentral.com
Meteorite-list mailing list
[email protected]
http://six.pairlist.net/mailman/listinfo/meteorite-list
______________________________________________
http://www.meteoritecentral.com
Meteorite-list mailing list
[email protected]
http://six.pairlist.net/mailman/listinfo/meteorite-list
