Thursday, February 27, 2014

Oldest known microscopic Zircon crystals confirms Earth's crust formation to 4.4 billion years ago

A very tiny Zircon crystals extracted from a remote rocky outcrop from Western Australia's Jack hills region has been confirmed to be formed 4.4 billion years ago - a recent study published in the journal Nature Geoscience

Prof. John W.Valley from University of Wisconsin-Madison spearheading a team of international scientist, have used a new technique called atom - probe tomography in conjunction with secondary ion mass spectrometer to establish accurately the age and thermal signatures of the zircon crystals by determining the mass of individual atoms of lead collected in the sample after radioactive decay of Uranium. The findings have been build on an earlier study by Prof. Valley and others, published in Nature journal that used lead isotopes to date zircon.

These tiny Zircon time capsules play an important role in radioactive dating of rocks, as they contain Uranium atoms, which sets the clock on as they start decaying into Lead. In addition they have also measured oxygen isotope ratios that sheds some light on the cooling of the Earth. This present findings will help in understanding formation of the Earth's hydrosphere and in understanding how other habitable planets form. 

Indeed we have come a long way from 4004 B.C. for the age of the Earth given by James Ussher to 4.4 billion years that comes out from this present study. 

Place of Jack hills zircon crystal (4.4 Ga) in context to the Earth's time - line.
Image credit: Andree Valley/ University of Wisconsin
Reference and Further Reading:
1. University of Wisconsin-Madison. "Oldest bit of crust firms up idea of cool early Earth." Sciencedaily. ScienceDaily, 23 February 2014.

2. John W. Valley, Aaron J. Cavosie, Takayuki Ushikubo, David A. Reinhard, Daniel F. Lawrence, David J. Larson, Peter H. Clifton, Thomas F. Kelly, Simon A. Wilde, Desmond E. Moser, Michael J. Spicuzza. (2014): Hadean age for a post-magma-ocean zircon confirmed by atom-probe tomography. Nature Geoscience.

3.Wilde, S. A., Valley, J. W., Peck, W. H. & Graham, C. M. (2001) Evidence from detrital zircons for the existence of continental crust and oceans on the Earth 4.4 Gyr ago. Nature 409, 175–178.