Electronic Resource
Palo Alto, Calif.
:
Annual Reviews
Annual Review of Earth and Planetary Sciences
33 (2005), S. 531-570
ISSN:
0084-6597
Source:
Annual Reviews Electronic Back Volume Collection 1932-2001ff
Topics:
Geosciences
,
Physics
Notes:
The Earth has a radiogenic W-isotopic composition compared to chondrites, demonstrating that it formed while 182Hf (half-life 9 Myr) was extant in Earth and decaying to 182W. This implies that Earth underwent early and rapid accretion and core formation, with most of the accumulation occurring in Đ♯10 Myr, and concluding approximately 30 Myr after the origin of the Solar System. The Hf-W data for lunar samples can be reconciled with a major Moon-forming impact that terminated the terrestrial accretion process Đ♯30 Myr after the origin of the Solar System. The suggestion that the proto-Earth to impactor mass ratio was 7:3 and occurred during accretion is inconsistent with the W isotope data. The W isotope data is satisfactorily modeled with a Mars-sized impactor on proto-Earth (proto-Earth to impactor ratio of 9:1) to form the Moon at Đ♯30 Myr.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1146/annurev.earth.33.092203.122614
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