Scientists identify a tiny piece of zircon that is 4.4b years old

Scientists using two different age-determining techniques have shown that a tiny zircon crystal found on a sheep farm in Western Australia is the oldest known piece of our planet, dating to 4.4 billion years ago.

Writing in the journal Nature Geoscience, the researchers said the discovery indicated that Earth's crust formed relatively soon after the planet formed and that the little gem was a remnant of it.

John Valley, a University of Wisconsin geoscience professor who led the research, said the findings suggested that early Earth was not as harsh a place as many scientists had thought.

To determine the age of the zircon fragment, the scientists first used a widely accepted dating technique based on determining the radioactive decay of uranium to lead in a mineral sample.

But because some scientists suggested that this technique might give a false date due to possible movement of lead atoms within the crystal over time, the researchers turned to a second sophisticated method to verify the finding.

They used a technique known as atom-probe tomography that was able to identify individual atoms of lead in the crystal and determine their mass, and confirmed that the zircon was indeed 4.4 billion years old.