Jamtveit and his colleagues carried out a grain-by-grain analysis of beach sand collected from two remote sites on the Mauritian coast. Their study revealed about 20 zircons that were far older than the rest of the sand.
The tiny crystals of zirconium silicate are exceedingly resistant to erosion or chemical change. The zircons found in the study had crystallized at least 660 million years ago, says Jamtveit. One of these zircons was at least 1.97 billion years old. The team chose to collect sand, rather than pulverize local rocks, to ensure that zircons inadvertently trapped in rock-crushing equipment from previous studies did not contaminate their fresh samples. The remote locations of the collection sites make it unlikely the zircons were carried there by humans.
The nearest known outcrop of continental crust that could have produced the Mauritian zircons is on Madagascar. It is suspected that the zircons were pulled up to the surface through volcanic activity on the island. “There’s no obvious local source for these zircons,” says Conall Mac Niocaill, a geologist at the University of Oxford, UK, who was not involved in the research.
Analyses of Earth’s gravitational field reveal broad areas where sea-floor crust is three to five times thicker than normal. They may be the remains of a landmass that the team has dubbed Mauritia, which they suggest split from Madagascar when tectonic rifting pushed the Indian subcontinent to the northeast millions of years ago. The researchers' study was published in the journal Nature Geoscience.