27
February 2003
Early Earth: Clocking on
The decay series from 176lutetium to 176hafnium is a powerful tool for studying early differentiation processes on Earth. 176Lu has a half-life of about 37,000 million years, making it a good chronometer for the period, and the fractionation of the daughter isotopes reveals details of crust–mantle separation. But this requires accurate knowledge of the radioactive decay of 176Lu, and of the bulk composition of the cooling planet. New data from chondritic meteorites provide a precise picture of Solar System Hf isotope content 4,560 million years ago, and a recalibrated 176Lu decay constant 6% faster than recent estimates. This suggests that a crust differentiated early in Earth's history, a mere 320 million years after planetary accretion.
Early history of Earth's crust-mantle system inferred
from hafnium isotopes in chondrites
MARTIN BIZZARRO,
JOEL A. BAKER, HENNING HAACK, DAVID ULFBECK & MINIK ROSING
Nature
421, 931–933 (2003); doi:10.1038/nature01421
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Geochemistry: Lost terrains of early Earth
STEIN B. JACOBSEN
Isotope data provide insight into the
earliest phases of terrestrial evolution. The latest reappraisal supports the
view that the early Earth had a cratered crust which crystallized from a magma
ocean.
Nature 421, 901–903 (2003); doi:10.1038/421901a
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