In Search of Earth’s Building Blocks

Two international research teams, including scientists from Freie Universität, have independently shown that the Earth partly consists of material that cannot be explained by known meteorite compositions. The studies appeared in Nature and Science. The most common type of meteorites that fall onto Earth are called chondrites, which represent little modified aggregates of dust from the early solar nebula. Therefore, it has long been assumed that chondrites represent the most plausible building material of the rocky planets. Evidence for a more complex composition of Earth's building materials now comes from examining the isotopic abundances of the rare earth element neodymium in representative Earth rocks in comparison to data from meteorites. The abundances of the neodymium isotopes Nd-142 and Nd-143 vary in nature mainly because they are formed by the decay of the radioactive samarium isotopes Sm-146 and Sm-147, respectively. Because of the short half-life of Sm-146, Nd-142 only increased during Earth's early history, but has not changed since then because all the atoms of Sm-146 have decayed.