Core formation during early accretion of the Earth.

Hf-W, ACCRETION OF THE EARTH, CORE FORMATION AND THE ORIGIN OF THE MOON. Stein

Introduction: The time scale and functional shape of Earth’s accretion and core formation may be investigated using the Hf (half-life: 9 Myr)-W extinct nuclide chronometer [1,2] because the Hf/W ratio is fractionated both strongly and uniquely by core formation. W is partitioned into the metal phase and Hf into the silicate mantle during the formation of the Earth. The core will develop a defic...

Isotopic constraints on the age and early differentiation of the Earth.

The Earth's age and early differentiation history are re-evaluated using updated isotopic constraints. From the most primitive terrestrial Pb isotopic compositions found at Isua Greenland, and the Pilbara of Western Australia, combined with precise geochronology of these localities, an age 4.49 +/- 0.02 Ga is obtained. This is interpreted as the mean age of core formation as U/Pb is fractionate...

The Osmium Isotopic Composition of Tagish Lake and Other Chondrites, Implications for Late Terrestrial Planetary Accretion

Introduction: The prevailing models for terrestrial planet origin and differentiation call upon magma oceans generally concurrent with core formation very early during differentiation. Tungsten isotope measurements of Earth and Mars materials are consistent with core formation occurring in terrestrial planets within 30 m.y. or less after the onset of condensation of the solar system [1-4]. In s...

Conditions of Core Formation in the Early Earth: Single Stage or Heterogeneous Accretion?

Highly siderophile element constraints on accretion and differentiation of the Earth-Moon system.

A new combined rhenium-osmium- and platinum-group element data set for basalts from the Moon establishes that the basalts have uniformly low abundances of highly siderophile elements. The data set indicates a lunar mantle with long-term, chondritic, highly siderophile element ratios, but with absolute abundances that are over 20 times lower than those in Earth's mantle. The results are consiste...