Gem of a find: Transmission light microscope image of Jack Hills zircons showing an angular diamond inclusion (dark, centre right).

Credit: Martina Menneken

Related articles

• Ancient diamonds push back age of life
• Diamonds are from outer space
• Nano-tools pick out traces of ancient life
• Meteor craters may hold untapped wealth
• Mars baked from different ingredients to Earth

SYDNEY: Four-billion-year-old diamonds have been discovered in Western Australia, they are almost as old as the world itself.

Found trapped inside crystals of zircon, the diamonds – which are just a few micrometres wide – add to evidence the planet was already cooling and the continental crust and oceans were forming as early as 4.4 billion years ago.

Until recently, experts believed that the Earth hadn't cooled enough for liquid water to form until three to four billion years ago.

A team of German and Australian researchers headed by Martina Menneken of University of Münster report the discovery this week in the U.K. journal Nature. The scientists dated the zircons using uranium and lead isotopes and that indicates that the diamonds are almost one billion years older than the previous terrestrial record holders. They are present in material that crystallized within 300 million years of the formation of the Earth itself.

Geologist's best friend

"The zircons were discovered 20 years ago and we've been extracting information ever since," said co-author Alexander Nemchin of Curtin University of Technology in Western Australia. Jack Hills, where the ancient rocks were found, is "the only place on Earth that can give us this kind of information about the formation of the Earth. We're dealing with the oldest material on the planet," he said.

Zircon crystals are tough and relatively resistant to melting – and thereby retain vital clues about the history of Earth's crust and mantle.

"Any information about the very early Earth is fantastic, it's like a Christmas present for geoscientists," said Martin Van Kranendonk, a senior geologist with the Geological Survey of Western Australia, in Perth. "This work provides a new constraint for geoscientists to consider how the Earth formed into the planet it is today. It's another piece in the early Earth puzzle."

Ian Williams a geologist at the Australian National University in Canberra commented that the recent studies add fuel to the debate about when the Earth began to cool sufficiently for water to condense. "[The] discovery that some of those ancient zircon crystals contain tiny diamonds turns the field on its head once more," he said.