New Zealand is earth’s eighth continent. Just mostly underwater.

I was all ‘woohoo’ last week when news broke that New Zealand is actually a continent about half the size of Australia, albeit mostly underwater. The discovery was published in the March-April issue of GSA Today in a paper authored by a team of New Zealand and New Caledonian geologists, including Nick Mortimer, Hamish Campbell, Peter R. Tulloch and others.

Zealandia today, as seabed, via Google Earth.
Zealandia today, shown as light blue seabed on Google Earth.

They argue that Zealandia classes as Earth’s eighth continent and stretches from the current New Zealand archipelago up to New Caledonia, which is another above-water bit of the whole. All of our offshore islands, right up to the Kermadecs, are encompassed by it. And yes, apart from the annoying problem of sea level, it puts us way ahead of Japan and more in league of Australia when it comes to continental scale stakes.

In a way it isn’t news. Zealandia has been visible on Google Earth ever since they started showing seabed contours, and well known to geologists for decades. The name itself was first proposed in 1995 by US geologist Bruce Luyendyk. I’ve been writing about this greater land in my own books since my 2004 general history, most recently in my 2014 science book on earthquakes (now out of print).

The difference is that Zealandia was never recognised as a continent in its own right and was always viewed as historical. The story is basically this: back in the late Cretaceous, ancient Gondwanaland began to break up. One slab – Zealandia – slid off to the east. Over the next tens of millions of years it eroded, progressively becoming a low-lying, swampy land mass – and then mostly disappearing altogether. By the Miocene period, some five million years ago, Zealandia was largely underwater: the New Zealand land mass consisted of a handful of isolated islands. There’s evidence of diverse speciation on the different islands, which is why several species of moa emerged.

But then the Australian and Pacific crustal plates collided, driving a new process of mountain-building, the Kaikoura orogeny.

Modern New Zealand emerged – very rapidly – from that process. Indeed, the Southern Alps are the fastest-rising mountains in the world. Had they not been eroded along the way, they’d be 20 km high by now. Other ranges also rose, which is why the Manawatu river cuts straight through a mountain range. The river was there first. This is an important point – conceptual maps of ‘Zealandia’ showing modern New Zealand in the middle of it aren’t correct. Modern New Zealand gained its shape well after Zealandia eroded.

Today the region is still tectonically active, which is why New Zealand has so many earthquakes and volcanic eruptions.

gsatg321a-1-f02
Map from the GSA Today paper

So why are we so excited about ‘Zealandia’ today? Well, Earth has fourteen crustal plates, and we differentiate between them by thickness. The thicker ones are continents, and all but Zealandia are above water. The thinner ones are seabed, and all of them are underwater. There are also many fragments of crustal plate, broken off and scattered underwater. Conceptually, it’s important to note that the actual above-below water point is arbitrary – the sea level changes over time, both because the land erodes (or rises) and because the sea level, itself, varies. What’s more important geologically is the nature of the underlying structure.

This is where the Mortimer, Campbell et al paper comes in. Their study argues that this eroded land-mass/sea bed system is a true continent – a thicker piece of crust than the crustal plates that make up the usual sea bed, and able to be considered a single entity. We always knew the shapes were there, underwater – it’s a technical adjustment in the way we classify it: and, like many technical adjustments, it’s created a shift in perspective and viewpoint.

How dramatic? Well, although the physical reality hasn’t changed one iota, if Zealandia is defined as a continent then New Zealand’s view of ourselves just got a whole lot bigger. It’s unlikely it’ll have any legal or practical effect – altering the size of our territorial waters, for instance. But it’s a conceptual vision that’s new. It also means Earth has eight continents, not seven. And, as I write this post, I also discover the definition is being disputed. Not everybody agrees with the proposal, and there isn’t an international body to officially determine how many continents Earth actually has.

All of which, to me, speaks far more about the way our world-view works, and how changes of perspective can create dramatic changes in behaviours, frameworks and conduct – all without a single thing changing in the empirical physical environment.

After all, Zealandia’s been around ever since the late Cretaceous. All that’s changed is the way we look at it. As the authors themselves pointed out in the paper, ‘Zealandia illustrates that the large and the obvious in natural science can be overlooked.’

And that, I think, is true of a lot of things about human endeavour. I’ll be extending that thought in next Monday’s post – but meanwhile, any thoughts on Zealandia?

Copyright © Matthew Wright 2017

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10 thoughts on “New Zealand is earth’s eighth continent. Just mostly underwater.

  1. How tragic for the Zealandia people. Those of us beyond its borders should launch a “Send a bucket to Zealandia” movement to help them reverse this terrible flood! 😉 Okay, more seriously…this sounds like Pluto all over again. Somewhere, those who study such things debate while the universe shakes its head and mutters, “Whatever.” Not to say it isn’t fascinating. It is. It’s a new perspective on our ever-changing world that’s full of lessons, not only about our physical world, but how human beings can find new ways to bicker. If it’s declared a continent does it then become ripe for colonization under rules differing from those existing? Uh-oh. Then again, maybe it’ll lead to a new continent classification. And now we’re back to Pluto again.

    1. It’s always intriguing how much of the way we ‘perceive’ things is framed by our ‘definitions’ of them – change the definition, and our perception changes. The Pluto issue always rankled me. Personally I think there are flaws in the whole astronomical classification system, because it insists on trying to draw hard borders between categories (dwarf planets, planets, stars, brown dwarfs etc) when really it’s more of a continuum. Continents seem to be the same thing. I’m quite delighted that NZ is a LOT bigger than it used to be, if a bit hard to travel to (I don’t think there’ll be a run on aqualungs though… 🙂 )

  2. Brilliant post Matthew. My other home is a hell of a lot bigger than previously thought. What happened to Zelandia has a parallel with what happened to Doggerland off the Uk’s East coast. Although in that case it was due to rising sea levels after the last Ice Age. I’ll be reposting this on my blog. 😉

    1. Thank you. Yes, it’s intriguing how our perceptions have changed – and the undersea shape was staring at us all along. I think it’s a great example of the way land-forms change, and Doggerland is the other – one (Zealandia) an instance of the way erosion without uplift can destroy a continent; and Doggerland a demonstration of the more immediate ways glaciation can raise or submerge the continental shelves. I guess it’s kind of lucky that our recent western world didn’t emerge while it WAS exposed, you can imagine the ease with which the Spanish could have walked into Elizabethan England, or the Kaiser or Hitler into London, if it wasn’t for the North Sea and the Channel. Although, as a flip-side, it would also have been possible – here – to walk from New Plymouth to Nelson, mostly through podocarp forest as I understand it. It’s all quite fascinating.

  3. As someone originally from the western part of terra australis i can safely say that that whole area was once below sea level for many many hundreds/thousands of years and the salt in our soil is mute testimony to that. So change is always with us and always will be. Finding past ones is interesting but does not change what now is.

    1. The way things are hasn’t changed at all with this discovery – but what has altered is the way we look at things, which for me is the interesting part. The story of the Eromanga Sea is curious because, although it covered much of what is now modern Australia, it didn’t alter the fact that Australia is a continental plate: so we have, in mid-Cretaceous times, essentially the mirror image of the current situation with Zealandia being underwater and Australia above. It underscores the arbitrariness of where water happens to go, relative to the two kinds of crustal plates that exist on Earth. I find that quite fascinating.

  4. Yes I quite agree with the fascination of learning about historical changes… one area that for me is even more fascinating is the tracing of connections between populations through linguistic commonalities and seeing how languages, both written and spoken evolve through population interceptions.

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