Gem is oldest piece of Earth

Scientists using two different age-determining techniques have shown that a tiny zircon crystal found on a sheep ranch in Western Australia is the oldest known piece of our planet, dating to 4.4billion 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 suggest that the early Earth was not as harsh a place as many scientists had earlier 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 hypothesised 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, which was able to identify individual atoms of lead in the crystal and determine their mass, and confirmed that the zircon was indeed 4.4billion years old.

To put that age in perspective, the Earth itself formed 4.5billion years ago as a ball of molten rock, meaning that its crust formed relatively soon thereafter, 100million years later.