How many continents are there on Earth? It all depends on your point of view. For many people, there are six: Europe, Asia, Africa, America, Oceania and Antarctica. However, some agree that Europe and Asia come together to form just one geological continent, Eurasia, whilst others class America as two separate ones, North America and South America.
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So there are at least five or six of them, at least that was the opinion until recently. But this could soon change following a study that was published in the Geological Society of America magazine. Led by a team of eleven researchers, the study revealed the existence of a previously unknown geological continent that has been named Zealandia.
According to geologists, this continent spreads over 4.9 million kilometres squared, just a bit bigger than India, and is hidden under the Pacific Ocean, around New Zealand and New Caledonia, hence the name Zealandia. This discovery may seem incredible, but it isn’t unexpected.
A collection of submerged islands and land
The Zealandia concept has already been discussed but hadn’t been identified as a real continent in the past. It lies under New Zealand, New Caledonia and a whole other collection of islands. With their new study, geologists show that all of these islands aren’t actually isolated but are connected by something submerged under the water.
'This is not a sudden discovery but a gradual realisation; as recently as 10 years ago we would not have had the accumulated data or confidence in interpretation to write this paper,' said the authors of the study. To reach this point, they considered all the criteria that would define a continent and then checked to see if they applied to Zealandia.
Overall, there are four main criteria to consider: the elevation of the land in comparison to the oceanic plate, a diversity of three types of rocks, a thicker, less dense section of crust and the size of the area in question. According to their conclusions, Zealandia seems to fill all the necessary characteristics.
Big enough and unfragmented
'This region has elevated bathymetry relative to surrounding oceanic crust, diverse and silica-rich rocks, and relatively thick and low-velocity crustal structure,' says scientists. Moreover, 'its isolation from Australia and large area support its definition as a continent.'
In other words, Zealandia is indeed big and unfragmented enough to be considered a full continent and not just a collection of submerged and isolated crust. According to calculations, Zealandia is most likely separated from Australia by a strip of ocean 25 kilometres wide but the largest part (94%) of the continent is probably submerged.
What also makes this continent distinctive is that it is part of two tectonic plates, the Pacific plate for its southern part, and the Australian plate for its northern. All this explains why it took scientists this long to identify it.
'The scientific value of classifying Zealandia as a continent is much more than just an extra name on a list,' says geologists.
A part of Gondwana
'That a continent can be so submerged yet unfragmented makes it a useful and thought-provoking geodynamic end member in exploring the cohesion and breakup of continental crust,' continue the authors of the study.
According to analysis done on rocks found there, Zealandia could be made from the same continental crust that is part of a supercontinent named Gondwana. It is possible that it migrated in a similar way to the Antarctic and Australian continents more than 100 million years ago before they got separated from each other. Today, Zealandia would also be 'the youngest and most submerged of Earth’s continents.'
When interviewed by Business Insider, Bruce Luyendyk, geophysicist from the University of California who isn’t involved in this study, said that it is very likely that the scientific community accepts the results of this study because it has 'a solid collection of evidence that’s really thorough.'
