Some Unanswered Questions from the Lunar Rocks

In the previous post I hinted that some of what we found from our study of moon rocks raises issues of self-consistency when viewed in terms of the standard paradigm. To summarize the relevant points of that paradigm, the argument goes that the dust in the accretion disk that was left behind after the star formed accreted into Mars-sized bodies that we shall call embryos, and these moved around in highly elliptical orbits and eventually collided to form planets. While these were all mixed up – simulations suggest what made Earth included bodies from outside Mars’ current orbit, and closer to the star than Mercury’s current orbit. These collisions were extraordinarily violent, and the Earth formed from a cloud of silicate vapours that condensed to a ball of boiling silicates at a little under 3000 degrees C. Metallic iron boils at 2862 degrees C, so it was effectively refluxing, and under these conditions it would extract elements such as tungsten and gold that dissolve in iron and take them with it to the core. About sixty million years after Earth formed, one remaining embryo struck Earth, a huge amount of silicates were sent into space, and the Moon condensed from this. The core of this embryo was supposedly iron, and it migrated into the Earth to join our core, leaving the Moon a ball of silicate vapour that had originated from Earth and condensed from something like 10,000 degrees C. You may now see a minor problem for Earth: if this iron took out all the gold, tungsten, etc, how come we can find it? One possibility is the metals formed chemical compounds. That is unlikely because at those temperatures elements that form only moderate-strength chemical bonds would not survive, and since gold is remarkably unreactive, that explanation won’t work. Another problem is that the Moon has very little water and no nitrogen. This easily explained through their being lost to space from the silicate vapours, but where did the Earth get its volatiles? And if the Moon did condense from such high temperatures, the last silicate to condense would be fayalite, but that was not included in the Apollo rocks, or if it were, nothing was made of that. This alone is not necessarily indicative, though, because fayalite is denser than the other olivines, and if there were liquid silicates for long enough it would presumably sink.

The standard paradigm invokes what is called “the late veneer”; after everything was over, Earth got bombarded with carbonaceous asteroids, which contain water, nitrogen, and some of these otherwise awkward metals. It is now that we enter one of the less endearing aspects of modern science: everything tends to be compartmentalised, and the little sub-disciplines all adhere to the paradigm and add small findings that support their view, even if they do not do so particularly well, and there is a reluctance to look at the overall picture. The net result is that while many of the findings can be made to seemingly provide answers to their isolated problems, there is an overall problem with self-consistency. Further, clues that the fundamental proposition might be wrong are carefully shelved.

The first problem was noted at the beginning of the century: the isotope ratios of metals like osmium from such chondrites are different from our osmium. There are various hand-waving argument to the extent that it could just manage if it were mixed with enough of our mantle, but leaving whether the maths are right aside, nobody seems to have noticed the only reason we are postulating this late veneer is that originally the iron stripped all the osmium from the mantle. You cannot dilute A with B if B is not there. There are a number of other reasons, one of which is the nitrogen of such chondrites has more 15N than our nitrogen. Another is to get the amounts of material here we need a huge amount of carbonaceous asteroids, but they have to come through the ordinary asteroids without perturbing them. That takes some believing.

But there is worse. All the rocks found by the Apollo program have none of the required materials and none of the asteroidal isotope signatures. The argument seems to be, they “bounced off” the Moon. But the Moon also has some fairly ferocious craters, so why did the impactors that caused them not bounce off? Let’s suppose they did bounce off, but they did not bounce off the Earth (because the only reason we argue for this is that we need them, so it is said, to account for our supply of certain metals). Now the isotope ratios of the oxygen atoms on the Moon have a value, and that value is constant over rocks that come from deep within the Moon, thanks to volcanism, and for the rocks from the highlands, so that is a lunar value. How can that be the same as Earth’s if Earth subsequently got heavily bombarded with asteroids that we know have different values? My answer, in my ebook “Planetary Formation and Biogenesis” is simple: there were no embryo impacts in forming Earth therefore the iron vapours did not extract out the heavy elements, and there were no significant number asteroid impacts. Almost everything came here when Earth accreted, and while there have been impacts, they made a trivial contribution to Earth’s supply of matter.