SCIENTISTS have set sail on a mission to uncover the secrets of the "lost continent" of Zealandia.

This gigantic landmass disappeared beneath the waves 75 million years ago - and it has never been explored.

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5 The drill ship Jodies Resolution sets sail to explore Zealandia Credit: AFP

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We know the dinosaurs died out 66 million years ago, so there is every chance scientists will find something totally unexpected in this drowned world.

It was originally part of the gigantic super-continent Gondwana, which was made up of many of the continents which now exist in the southern hemisphere.

Covering 1.9 million square miles, it extends from south of New Zealand northward to New Caledonia and west to the Kenn Plateau off Australia's east coast.

Drill ship Joides Resolution will recover sediments and rocks lying deep beneath the sea bed in a bid to discover how the region has behaved over the past tens of millions of years.

The recovered cores will be studied onboard, allowing scientists to address issues such as oceanographic history, extreme climates, sub-seafloor life, plate tectonics and earthquake-generating zones.

Co-chief scientist Jerry Dickens, from Rice University in Texas, said the region was a vital area to study changes in global climate.

5 New Zealand sits atop a previously unknown continent—mostly submerged beneath the South Pacific Credit: GSA Today

5 The continent would have been the size of greater India Credit: GSA Today

5 Scientists have spent 20 years trying to prove Zealandia's existence Credit: GSA Today

"As Australia moved north and the Tasman Sea developed, global circulation patterns changed and water depths over Zealandia fluctuated," he said.

"This region was important in influencing global changes."

In a paper published in the Geological Society of America's Journal GSA Today in February, researchers also made the case that it should be considered a new continent.

They said it was a distinct geological entity that met all the criteria applied to Earth's other continents, including elevation above the surrounding area, distinctive geology, a well-defined area and a crust much thicker than that found on the ocean floor.

Australian National University's Neville Exon said the two-month expedition, setting out Friday from Townsville, would also help better understand major changes in the global tectonic configuration that started about 53 million years ago.

What is a continent? The Glossary of Geology defines a continent as "one of the Earth’s major land masses, including both dry land and continental shelves" (Neuendorf et al., 2005). Continents must have high elevation relative to regions floored by oceanic crust; a broad range of siliceous igneous, metamorphic, and sedimentary rocks; thicker crust and lower seismic velocity structure than oceanic crustal regions; and well-defined limits around a large enough area to be considered a continent rather than a microcontinent or continental fragment. Europe, Asia, Africa, North America, South America, Antarctica, and Australia are all bonafide continents.

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This is around the time that the Pacific "Ring of Fire", a hotspot for volcanoes and earthquakes, came into existence.

In the February scientific paper, lead author Nick Mortimer said experts had been gathering data to make the case for Zealandia being a continent for more than 20 years.

But their efforts had been frustrated because most of it was hidden beneath the waves.

"If we could pull the plug on the oceans, it would be clear to everybody that we have mountain chains and a big, high-standing continent," he said at the time.

It follows the discovery of a gigantic “lost continent” called Mauritia hidden beneath the island of Mauritius.