Diamonds used to ‘probe’ ancient Earth

Diamonds dug up from ancient rock formations in South Africa, between 1890 and 1930, have unveiled secrets of how the Earth was shaped more than 3.5 billion years ago, a new study has found.

The three diamonds extracted from Witwaters-rand Supergroup, the rock formation that is host to the famous Johannesburg gold mines, were investigated by researchers from the University of Johannes-burg, Wits University in South Africa and Univers-ity of Alberta in Canada to study when modern-style plate tectonics began to operate on planet Earth.

The Earth is approximately 4.5 billion years old, and while a rock record exists from about 4 billion years ago, the complex preservational history of the most ancient rocks exposed on Earth’s surface has led to a heated debate among scientists on when plate tectonics began operating on Earth. Many researchers believe plate tectonics began in the Archaean (the Eon that took place from 4 to 2.5 billion years ago), although the exact timing is highly contested. While the diamonds of this study were found in 3 billion-year-old sedimentary rocks, diamond formation occurred much deeper, within Earth’s mantle. Additionally, based on the nitrogen characteristics of the diamonds, they also formed much earlier, around 3.5 billion years ago.

Transport of the diamonds to the surface of the Earth by kimberlite-like volcanism, followed by their voyage across the ancient Earth surface and into the Witwatersrand basin, occurred between 3.5 and 3 billion years ago. Researchers used an ion probe to analyse the carbon and nitrogen isotope compositions of the Witwater-srand diamonds, which have been pristinely preserved for more than three billion years.