KREEP and the Magma Ocean

  1. Ian James Miller

    The standard theory of planetary formation asserts that the final stage of planetary formation involves the collision of massive bodies, and the overall result is a magma ocean due to the energy of the collision. Either planets were formed this way or they were not. If they were, all rocky planets would presumably have such a magma ocean that would slowly cool and solidify. We believe the Moon had such a molten state, and as it cooled, one of the last stages involved the laying down of KREEP (containing potassium, rare earth elements and phosphate). As I understand it, the reason this formed was that this had the lowest melting point, and thus phase separated and remained fluid while general silicates solidified.

    From general physical chemistry, and for that matter experience with multiphase systems, phase separation is more likely to arise the longer the system stays in a fluid state. Therefore, if planets had a magma ocean, similar phase separation should have arisen, and with more of it. However, there is no evidence that it did. We can find large areas of plagioclase on Mars, but no KREEP. We can find no deposits of the weathered remains of such KREEP on Earth either as phosphate deposits of rare earths, or as rare earth clays. (Rare earths are not that rare; what is rare is to find any evidence of concentration of them from bulk rock.)

    Either there was a magma ocean or there was not. If not, the standard model of planetary formation seems to be in serious trouble, since it always invokes said magma ocean. If the standard model is wrong, all predictions of planets and their properties based on it are unreliable. If there really were magma oceans, what happened to the KREEP? Either it formed or it did not. If it did, what happened to it? If it did not, why not?

  2. Helen M.

    I was not aware of it.. But now I am curious to know more about it, what it is and what happen next. Also share with me if you come to know any other information… Thanks in advance