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ROCK from the Earth’s infancy has been found in Australia. Radiometric dating
suggests a tiny crystal of zircon is a record 4.4 billion years old. Much to the
surprise of geologists, the ratio of oxygen isotopes shows that the zircon
formed in contact with liquid water (Nature, vol 409, p 175 and 178).
The conventional view is that the Earth was then too hot for liquid water to
exist, says John Valley of the University of Wisconsin in Madison.