The ancient zircons recovered in the new research are the only accessible remnants of the old granitic rocks which are now hidden below. We cannot specify the exact size of the buried fragment of ancient continent, but we think it might be similar to the present areal extent of Mauritius, about 2000kmsq.

In addition to our discovery of this previously unknown continental fragment below Mauritius, my colleagues and I suggest that there may be other pieces of ancient continent scattered elsewhere on the floor of the Indian Ocean. These are now mostly submerged and covered by lavas, coral reefs or sand banks. They include the Saya de Malha Bank, the Chagos and Cargados-Carahos shoals, the Laccadive Ridge and the Nazareth Bank. They may have once been joined together 80 to 90 million years ago, in a now fragmented continent we have named “Mauritia”.

Continental break up

So, where did this all begin?

We have known for some time that the familiar continental entities of the southern hemisphere – including Africa, South America, Madagascar, India, Australia and Antarctica – were joined together about 500 million years ago. This huge landmass was called Gondwana. In fact, Gondwana was once part of an even larger “super-continent” called Pangea.

About 185 million years ago Gondwana began to drift apart and fragment due to plate tectonic processes that take place at the Earth’s outer shell of crustal rocks. Pieces of continent, both large and small, ride as “passengers” on newly-formed plates of oceanic crust; these continuously move away from each other at speeds of several centimetres per year.

The familiar present-day positions of the continents will continue to change, as plate tectonic forces drive them apart. For example, continental fragmentation appears to be starting in the East African Rift of Ethiopia, Kenya and Tanzania, where a new ocean basin might form tens of millions of years in the future, splitting East and West Africa into separate continental pieces.

In this sense, the idea that there are only seven continents is misleading because it is arbitrarily based on size, and would exclude substantial continental entities like Greenland and Borneo, as well as smaller ones like Madagascar, New Guinea and New Zealand. Because the sizes and shapes of continents have continuously changed over time, all continental entities can therefore be considered “fragments” of variable size.

It isn’t every day that someone can claim to have discovered a new piece of continent, even though the one in the new work described here is buried under a volcano and cannot be seen or touched. But its presence adds to a growing understanding of how the Earth works at present, and contributes to the question of how it worked in the past. These are the primary goals of geological science.

Lewis Ashwal, Professor, University of the Witwatersrand

This article was originally published on The Conversation. Read the original article.

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