[meteorite-list] A question????? another answer
From: Mr EMan <mstreman53_at_meteoritecentral.com>
Date: Fri, 5 Jun 2009 20:58:50 -0700 (PDT)
You are too kind, Carl. Let me address your questions inside your quote:
--- On Fri, 6/5/09, cdtucson at cox.net <cdtucson at cox.net> 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
Received on Fri 05 Jun 2009 11:58:50 PM PDT