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.
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.
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