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Take a look at http://carnegieinstitution.org/news_980917.html

Interesting paper, but doesn't really make a difference to the Moon/Earth compositional difference. It's just saying that the "C1 model" doesn't hold for Mars. If it didn't hold for the moon, then maybe that's because it lost a lot of it's native material during the Earth/Theia impact, and Theia did fit the C1 model--or not. Or maybe the moon is captured, and it does or it doesn't fit the C1 model.

Conservation of Angular Momentum would play an important role, so and the direction that the proto-moon blobbed out would be fairly aribitrary, so I would guess it just turned out that the earth ended up with an AM vector pointed at 23.5 degs to the ecliptic.

This is my problem. If angular momentum is being conserved, and if the tilt of the axis is even half of where it is now then one would expect the moon to follow an orbit near the celestian equator at the time it separated.

Yeah, I see what you're saying, but (a), what I said before, I don't know what tidal forces can do to these things, specifically the inclination of the proto-moons orbit, and (b), maybe Theia hit at the right trajectory to give the proto-Earth/Theia blob a tilt of about 23 degrees, and then a little bit (say 5%) into a low inclination orbit, maybe following the original trajectory of theia, of which 1.2% became the moon (yep, the moon is 1.2% of the mass of the Earth). This would make hardly any difference to the Earth-Theia blob's AM, so it may have nudged the vector up or down a bit. I think that's another of the successes of the Earth/Theia theory, it accounts for the axial tilt of the earth, and the Moon's orbital properties don't really come into that.

Anyway, good chatting, I think I've said enough.

Interesting, what are the setbacks?


Take a look at http://carnegieinstitution.org/news_980917.html

The basic problem is that the iron/silicon ratios of C1 carbonaceous chondrite meteorites matches the composition of the earth, but new data from the Pathfinder is raising doubts as to whether Mars has the same ratios (as previously thought). If this data continues to hold up it means that C1 carbonaceous chondrites may have helped form Earth, but Mars joins Mercury as an inner planet not formed from them. And as we lack sufficient data from Venus to say for sure, a theory which has been the mainstay of 40 years seems somewhat in peril.

The moon and the earth have the same Oxygen isotope ratios, which supports the impact theory.

Indeed it does seem to support that theory over a coformation theory. However, given the way these are calculated, I don't have enough information to comment further (most of these are the 16Oxygen(16O)/17O v. 16O/18O and plotting this as a line. Though it seems to me that regardless of which theory one wants to support, I would expect the rocks to be fairly rich in 16Oxygen, either due to centrigul action or due to reactions with warm ocean water).

Conservation of Angular Momentum would play an important role, so and the direction that the proto-moon blobbed out would be fairly aribitrary, so I would guess it just turned out that the earth ended up with an AM vector pointed at 23.5 degs to the ecliptic.

This is my problem. If angular momentum is being conserved, and if the tilt of the axis is even half of where it is now then one would expect the moon to follow an orbit near the celestian equator at the time it separated. I don't see tidal forces being that great in in these cases. But I could be wrong. Now, tidal forces combined with a maliable proto-moon could account for the spherical shape.

Just some thoughts...

Pictures and the press release.

Pictures and the press release.

http://carnegieinstitution.org/news_releases/news_ 040913.html

You should keep a more open mind... Science is all about theories, and we're not completely certain that oil comes from fossils...

It may, in fact be created by Intelligent Design. Well, that or some complex process of pressure turning carbon into oil, sort of like how diamonds come from pressurized carbon but yet completely different. :-)