A geological controversy over how a 2700-million-year-old rock was formed has been solved using synchrotron technology, an international team reports.

The team reports in the latest Nature journal that a rare form of magmatic rock known as komatiite was formed in the earth's mantle at temperatures around 1700°C in the Archaean age, more than 2700 million years ago.

Australian co-author Associate Professor Leonid Danyushevsky, at the Australian Research Council Centre of Excellence in Ore Deposits at the University of Tasmania, says the finding settles a long-disputed controversy over the volcanic rocks origin.

The first "hot-melting" model assumes the komatiite was formed through the melting of a mantle source at temperatures up to 500°C hotter than today's mantle temperature.

Under the second "wet-melting" theory komatiites were formed at temperatures only slightly higher than today's mantle temperature and cooled by the presence of water.