At http://phys.org/print393166825.html … a new study seems to contradict the tenant the composition of the earth should not differ too greatly from primitive chondrite meteorites. The latter are considered to date back to the formation of the solar system – and theoretically were formed contemporarily with the earth. The idea is supported by several neodymium (Nd) isotopes and the occurrence of them in meteorites and in bulk silicate on the earth. Some ten years ago it was found rocks on earth had a higher abundance of 142Nd than that found in chondrite meteorites and several reasons for this were aired (and adopted as assumptions by their peers). One idea was that earth's mantle had a hidden reservoir of of the parent isotope 146smarian (Sm) which decayed to 142Nd. This idea has now been shown to be wrong and the difference is down to nucleosynthetic processes instead (until somebody has a better idea). We are informed the discovery has 'implications for our understanding' of the earth, not just for determining its bulk composition but also for 'constraining the modes and timescale' of its geodynamical evolution. That sounds interesting- but what do they really mean?