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Zealandia – pieces finally falling together for continent we didn’t know we had

Zealandia – a new continent submerged in the southwest Pacific – is a step closer to being recognised, the authors of a new scientific paper claim.

A paper published in GSA Today, the journal of the Geological Society of America, contends that the vast, continuous expanse of continental crust, which centres on New Zealand, is distinct enough to constitute a separate continent.

The paper’s authors argue that the incremental way in which it came to light goes to show that even “the large and the obvious in natural science can be overlooked”.

Zealandia covers nearly 5m square km, of which 94% is under water, and encompasses not only New Zealand but also New Caledonia, Norfolk Island, the Lord Howe Island group and Elizabeth and Middleton reefs.

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A map showing the outline of Zealandia Photograph: GNS Science

The area, about the same size as the Indian subcontinent, is believed to have broken away from Gondwana – the immense landmass that once encompassed Australia – and sank between 60m and 85m years ago.

“This is a big piece of ground we’re talking about, even if it is submerged,” said Nick Mortimer, a New Zealand geologist who co-authored the paper.

Geologists have argued in favour of Zealandia being recognised as its own continent intermittently over the past 20 years.

The American geophysicist Bruce Luyendyk was the first to apply the name Zealandia to a south-west Pacific continent in 1995. Since then, the paper’s co-authors say, it has had “moderate uptake” but was still not broadly known to international scientists.

Mortimer and his fellow co-authors from the GNS Science research institute and Victoria University of Wellington in New Zealand; the Service Géologique of New Caledonia; and the University of Sydney’s School of Geosciences contend that Zealandia has the necessary geological elements to be considered a continent.

Mortimer told Guardian Australia that it was the first robust, peer-reviewed scientific paper to define and describe Zealandia, but its findings would offer “nothing new” for most New Zealand geoscientists. “They probably wonder what all the fuss is about.”

He said he and other researchers began to piece together the submerged continent with the release of a bathymetric map in 2002.

“That’s when the penny dropped, really … From that point, that map was literally our road map for some crosses, just trying to get rocks out of all the four corners of Zealandia that we could, so we could prove up the geology.”

There had been no formal Zealandia project, he said; it had been “a gradual process … [of] joining the dots”.

“It was a question of confidence, fundamentally, I think, with the accumulation of data and what to do with it.”

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Zealandia shown on a map of world continents. Photograph: GNS Science

Zealandia would be the world’s seventh and smallest continent, after Eurasia, Africa, North America, South America, Antarctica, and Australia. (Europe and Asia are sometimes recognised separately, despite being the same landmass.)

“It turns out New Zealand isn’t just a couple of small islands at the bottom of the world,” Fairfax Media New Zealand triumphantly reported.

Barry Kohn, a professor of earth sciences at the University of Melbourne, who had done work with Mortimer on Zealandia in the past, said there was a “fair consensus in the scientific community” in favour of its existence.

“It’s pretty clear that that whole area is not part of the ocean. It’s got all the hallmarks of a continent.”

He said rock dredged up from the area was clearly continental crust, “fairly continuous” and defined. More data had been gathered over the past decades to confirm its existence.

“Like anything in science, the penny doesn’t always drop straightaway. You build up a body of evidence.

“It was all once part of a big continent that’s all broken up into little pieces of the puzzle.”

But despite the evidence in support of it, whether or not Zealandia would come to be widely recognised as the seventh continent was dependant on history, said Mortimer.

“If you want to name a mountain, there are certain procedures you have to go through to get it formally ratified. With this, it will just come with time.

“If Zealandia makes its way into popular culture and onto maps, that’s all the validation that we’ll seek.”

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