RT Journal Article
SR Electronic
T1 Evolution of Planetary Cores and the Earth-Moon System from Nb/Ta Systematics
JF Science
JO Science
FD American Association for the Advancement of Science
SP 84
OP 87
DO 10.1126/science.1084662
VO 301
IS 5629
A1 Münker, Carsten
A1 Pfänder, Jörg A.
A1 Weyer, Stefan
A1 Büchl, Anette
A1 Kleine, Thorsten
A1 Mezger, Klaus
YR 2003
UL http://science.sciencemag.org/content/301/5629/84.abstract
AB It has been assumed that Nb and Ta are not fractionated during differentiation processes on terrestrial planets and that both elements are lithophile. High-precision measurements of Nb/Ta and Zr/Hf reveal that Nb is moderately siderophile at high pressures. Nb/Ta values in the bulk silicate Earth (14.0 ± 0.3) and the Moon (17.0 ± 0.8) are below the chondritic ratio of 19.9 ± 0.6, in contrast to Mars and asteroids. The lunar Nb/Ta constrains the mass fraction of impactor material in the Moon to less than 65%. Moreover, the Moon-forming impact can be linked in time with the final core-mantle equilibration on Earth 4.533 billion years ago.