Geology: A chip off the old continent

Zircon-containing rocks and a sample of zircon, showing the pits produced by analysis of oxygen and lead isotopes (from Mojzsis et al.).

The oldest known rock formations on Earth date to about 4,000 million years ago, around the time that the intense meteor bombardment abated. But glimpses of an even earlier time can be obtained from tiny grains of zircon — a mineral that is incredibly resistant to high pressures and temperatures and so could survive the early bombardment period unchanged. Two groups this week report new isotopic analyses of zircons from the Narryer Gneiss Complex in Western Australia. The measurements suggests that these samples are older than any terrestrial grains previously identified on Earth, and are consistent with the presence of continental; crust and liquid water on the Earth's surface between 4,400 and 4,300 million years ago.

Evidence from detrital zircons for the existence of continental crust and oceans on the Earth 4.4Gyr ago
SIMON A. WILDE, JOHN W. VALLEY, WILLIAM H. PECK, COLIN M. GRAHAM
Nature 409, 175-178 (11 January 2001)
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Oxygen-isotope evidence from ancient zircons for liquid water at the Earth's surface 4,300Myr ago
STEPHEN J. MOJZSIS, T. MARK HARRISON, ROBERT T. PIDGEON
Nature 409, 178-181 (11 January 2001)
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Earth science: In the beginning. . .
ALEX N. HALLIDAY
Grains of the mineral zircon have survived from way back in Earth's history. Analysis of these grains provides information on the state of our planet as long as 4.4 billion years ago.
Nature 409, 144-145 (11 January 2001)
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11 January 2001 table of contents