It was always there, drowned under the vast ocean, our little country its only visible point.

Scientists had known about it for decades, but were reluctant to state, unequivocally, that the lost continent of Zealandia physically existed.

But it did; and for a relatively brief point in the Earth's history its sprawling mass once stood above the waves, dispersing animals and plants from here to New Caledonia and the east of Australia.

Picture a dark green world of ancient forests, much like northern New Zealand today, teeming with a colourful abundance of insects, birds, mammals and reptiles.

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Most groups of dinosaurs, including the towering titanosaurs, roamed its rolling, mountainless, low-lying landscape.

Ninety-four per cent of it now lies underwater.

But if we drained the oceans, we could see it unfurling some 4.9 million sq km across the South Pacific.

Zealandia is the world's the world's youngest, smallest, thinnest and most submerged continent. Photo / Supplied
Zealandia is the world's the world's youngest, smallest, thinnest and most submerged continent. Photo / Supplied

Scientific papers and reports hinted at the presence of an eighth continent, spanning right back to 1910, when improved bathymetric maps showed our country wasn't just a few chunks of land jutting from an otherwise deep bath of abyssal ocean crust.

By the mid-2000s, GNS Science geologists including Dr Hamish Campbell and Dr Nick Mortimer began publishing research describing Zealandia's physical boundaries and make-up.

It wasn't until this year that a paper, led by Mortimer, somehow made Zealandia a real place.

Here was the world's freshest, smallest, thinnest and most submerged continent.

The revelation instantly captured the world's imagination, generating more than 16,000 news articles that reached nearly a billion people.

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Next to the detection of cosmic waves created by the collision of two neutron stars and the fiery death of Nasa spacecraft Cassini amid Saturn's atmosphere, the final "discovery" of Zealandia stands as one of the big science stories of 2017.

Looking back, Mortimer said no one had figured that what he considered a fairly ordinary press release from the Geological Society of America would trigger such an explosion of publicity.

A fish-eye view of Zealandia on the globe. Photo / Supplied
A fish-eye view of Zealandia on the globe. Photo / Supplied

When it made Mortimer a fellow last month, New Zealand's Royal Society Te Aparangi, too, stated that such extraordinary global interest was rare for our country.

"Our response was a mixture of surprise and delight," Mortimer said.

Since arriving here from Britain in the mid-1980s, his work has drifted slowly toward Zealandia, by way of every geologist's great fascination: Gondwanaland.

When that vast supercontinent broke up into five continent-sized pieces, it created South America, Africa, Antarctica, India, Australia — and Zealandia.

This happened progressively from 150 to 50 million years ago, somewhat like a reverse jigsaw puzzle, but leaving buried clues to help geologists piece it back together.

One giveaway was Zealandia's geology, with its older foundations of granites and greywackes, and cover of younger sedimentary and volcanic rocks, which was strikingly similar to that of its former neighbours Australia and Antarctica.

GNS Science geologist Dr Nick Mortimer was recently honoured by the Royal Society Te Aparangi for his part in the final recognition of Zealandia. Photo / File
GNS Science geologist Dr Nick Mortimer was recently honoured by the Royal Society Te Aparangi for his part in the final recognition of Zealandia. Photo / File

The time-frame of Zealandia's separation from Gondwana, and eventual plunge into the ocean, has been revised as new geological evidence has come to light.

This has told us that for at least 400 million years, up to about 100 million years ago, the Pacific Plate was subducting beneath the eastern edge of the ancient continent of Gondwana.

Sediments piled up along the margin of the continent and became crumpled and deformed as they were squeezed into greywacke and schist by the colliding plates.

About 100 million years ago, the tectonic situation changed again, when Gondwana was stretched and rifted, eventually separating off a large fragment that became Zealandia.

First, it was all land, but then it slowly sank as the Tasman Sea grew, and it continued to be stretched and thinned until about 25 million years ago, when it was mostly under the sea.

Whether all of it fell below the surface has long been historically debated by scientists, but fossil evidence and living enigmas such as tuatara and kauri suggest that some small Zealandia islands survived the great drowning.

A chronology of the break-away and evolution of Zealandia. Photo / Supplied
A chronology of the break-away and evolution of Zealandia. Photo / Supplied

And even if just 1 per cent of Zealandia stayed dry, that would still represent more than 2500 sq km - an area scientists have pointed out is well over 1000 times the surface area of Stephen's Island, where more than 30,000 tuatara currently live.

Studying modern-day Zealandia was difficult for the obvious reason that most of it lies more than a kilometre below the sea.

But the good news was that, once sunken, it changed very little, offering an incredible 60-million-year window into "history before history".

"The reason is that the process of erosion is negligible under the sea compared with on land," Mortimer said.

"So whatever rocks are there stay there locked up and don't get eroded away like they do in New Zealand and New Caledonia.

Zealandia is the planet's smallest continent. Photo / Supplied
Zealandia is the planet's smallest continent. Photo / Supplied

"The trade-off is that they become less accessible to our oxygen-breathing species and we have to launch marine seismic, dredging and drilling expeditions to study the undersea rocks."

One nine-week, 12-nation drilling expedition this year retrieved more than 8000 specimens from the depths, along with several hundred fossil species, that revealed it was much closer to land level than previously believed and shallow enough to offer pathways for animals and plants to move along.

Most importantly, the records showed the geography and climate of Zealandia were dramatically different in the past, offering a new, sensitive test for computer models being used to predict future changes in climate.

GNS Science geologist Dr Hamish Campbell has helped shed new light on Zealandia. Photo / File
GNS Science geologist Dr Hamish Campbell has helped shed new light on Zealandia. Photo / File

"As a geologist you realise that tectonics, climate, sea-level, species extinction and evolution have naturally changed between far wider extremes than we are currently experiencing," Mortimer said.

"If Zealandia can help educate non-scientists, politicians, and laboratory and theoretical scientists that natural variation and change is normal, to be embraced, and not in itself a threat then I think that will be useful.

"Zealandia's all about providing a new context and perspective."

He liked to think the big Zealandia questions of what, where and when, mostly, had all been answered over the past 20 years.

"In the future, we can move on to the more interesting, process-oriented scientific questions of how, why and the details of when.

"How and why did Zealandia get to be the world's smallest, thinnest, youngest continent — without shredding itself into tiny microcontinent-sized pieces as happened to Madagascar, Mauritia and other fragments in the Indian Ocean?

Tuatara are often suggested as living proof that the whole of Zealandia never sank, but scientists remain in debate over the question. Photo / File
Tuatara are often suggested as living proof that the whole of Zealandia never sank, but scientists remain in debate over the question. Photo / File

"For the biologists and palaeontologists we've delivered them a clean, well-defined Zealandia template on which to place their work.

"It's up to them to make something of that; species development on a shrinking continent."

For the rest of us, Mortimer hopes Zealandia will claim its rightful place in general knowledge.

"I'd love to see Zealandia in schools. In casual conversation many people have heard of Zealandia.

"We promote Zealandia as Continent Eight."

Discovering our lost continent

1910s:

New Zealand Plateau recognised as bathymetric maps became more accurate. The shallow water aspect was very important and first indicated that NZ was not surrounded by deep, abyssal oceanic crust.

1920s-1980s:

The term "continental crust" is often used in scientific papers when describing geology in the region.

1995:

A paper published by US marine geophysicist Bruce Luyendyk makes the first reference of Zealandia as a submerged continent, but only in passing.

2004-2008:

First GNS Science papers describing Zealandia's boundaries and geology; Zealandia increasingly gets used in scientific literature as convenient term for the continent.

2014:

Nick Mortimer and Hamish Campbell's book

Zealandia: Our Continent Revealed

is published.

2017:

A paper led by Mortimer and published in a US journal is published and attracts massive publicity, finally acknowledging the existence of an eighth continent.