Editorial: New Zealand is the highest ridge of geologically defined continent

Cape Reinga, Northland. Photo / Tania Whyte

For 80 million years the truth was under our feet. Who would have guessed that New Zealand is the most visible part of a hidden continent?

It is, and always has been, according to a team of scientists from New Zealand, Australia and New Caledonia.

The idea that New Zealand was sitting on top of a submerged continent has been around a while, and the name given to the newcomer, Zealandia, was attached to a southwest Pacific mass more than 20 years ago.

What is different now is that science has the tools such as gravity maps to assemble all the bits of geological evidence which, taken together, fulfil the requirements for Zealandia to be considered a bona fide continent.

Rather than a collection of continental fragments, the region is a single, intact chunk of continental crust isolated from the continent of Australia.

It stretches from a little north of New Caledonia to the continental shelf around the Campbell Plateau, an underwater triangle 1200 kilometres south of New Zealand. Just 25km separates Zealandia from its closest point to northern Australia, but a deep 3600 metre trench known as the Cato Trough divides them.

Nearly 5 million sq km in area (about the size of India) Zealandia is both the newest and smallest of the world's continents.

The forces which shaped its outline ensured that nearly all its surface is below sea level. The rift that split the mass from the immense supercontinent Gondwana thinned the crust, leaving just New Zealand and New Caledonia as the biggest bits above water.

The case for Zealandia is perhaps counter-intuitive because the term ''continent'' conveys the idea of a very large and obvious landmass with coastlines that stretch for thousands of kilometres. The work of the Zealandia scientists challenges this convention, especially the prevailing view that the existing continents cover all the major parts of the planet.

In other words, there was nothing else to see before the Zealandia geologists peered a bit closer.

The new study in the Geological Society of America journal remarks: "Zealandia illustrates that the large and the obvious in natural science can be overlooked."

The researchers say that a submerged, unfragmented continent made it useful for "exploring the cohesion and break-up of continental crust."

Adding weight to the idea of Zealandia as a continent is that the whole area is well above the adjacent oceanic crust, though still beneath the sea surface.

By convention the globe has seven continents: Europe, Asia, Africa, Antarctica, Australia, North America, South America.

Geologists count six, combining Europe and Asia as Eurasia. Recognition of Zealandia would add one more, although there is no accepted mechanism for the continental club to accommodate an additional member.

Science gets nudged from time to time to change orthodox understandings.

A recent example was Pluto, which in 2006 was struck from the list of planets because it was too small and redesignated a "dwarf planet." Zealandia left Gondwana around 60 million to 85m years ago.

Let's hope it doesn't take that long to work its way into popular culture to stand alongside the world's other continents.