BELOW THE INDIAN Ocean, a continent has lain hidden for millions of years, but now its presence has been revealed by grains of sand lying on a beach. What’s more, geologists believe there could be lots of these ‘ghost continents’ scattered around the globe waiting to be discovered.
When an international team of geologists analysed sand from the beaches of Mauritius, an island in the Indian Ocean, they found zircon crystals ranging from 660 million to nearly two billion years old. But Mauritius is a much younger, volcanic island – its oldest rocks are no more than 8.9 million years old.
These zircon crystals (‘zircons’) are also much older than any sea floor crust on the planet, so the researchers suggest the zircons were dragged up from an ancient landmass that once linked India and Madagascar -volcanic activity bringing them to the surface, where they mingled with the island’s sands.
To test this idea they looked at maps of the Earth’s gravitational field, which reveal the thickness of the Earth’s crust.
They identified a banana-shaped sliver of unusually thick crust under the Indian Ocean. This crust, they say, could be the remnants of the microcontinent they have named ‘Mauritia’, which broke apart when India and Madagascar started to go their separate ways 85 million years ago.
“Lots of other oceanic islands could be sitting above drowned microcontinents,” says Dr Hans Amundsen, a geologist who runs the Norwegian company Earth and Planetary Exploration Services and who was involved with the research.
“The Canary Islands and Madeira in the Atlantic Ocean are two possible candidates. To find out, scientists need to look for old zircons that have survived their travels to the surface,” says Amundsen. “I think we’re going to find more.”