How many continents are there on Earth? Seven right? Well, actually it is, but only for geologists or is it now five? Contrary to common practice, geologists tend to group Europe and Asia into one super-continent called Eurasia. You can also include Africa to make a four continent world as well, and the Americas into one. But fear not, their historic total of six, or is it four, is also apparently wrong. A new study might just mean that current geography textbooks need to be thrown out. Welcome the Earth's brand new, well newly discovered, continent 'Zealandia'.
Let's take a quick look at the new "kid on the block" in the continent club.
[Image Source: Aenigmatis-3D via Pixabay]
So what is a continent anyway?
For geologists, continents are areas of the Earth's crust with a substantially different composition, density and thickness when compared to thinner and denser oceanic crust. Continents tend to comprise of sedimentary, igneous and metamorphic rocks compared to the mainly igneous rocks of oceanic crust. The mixture of these attributes of continental crust has meant that they have stood the test of time. Oceanic crust is so heavy, relatively, it tends to be subducted underneath the less dense and more buoyant continental crust.
Non-geological classical divisions tend to be along ethnocultural divisions rather than geography per say but this isn't a hard and fast rule. In geology, however, defined continents have very little real meaning. For instance, the current configuration of continents is the product of millions of years of tectonic bumper cars. Around 300 million years ago, they were all joined together into the Pacman inspired Pangea and continued to move. India was once a separate continent before plowing, rather gracefully, into Asia to form the Himalayas. So you know, all things are in flux.
[Image Source: Wikimedia Creative Commons]
Ok, so what's the big deal?
The new study of the Earth's crust seems to provide evidence of a new, as yet unappreciated continent. It has literally been hiding under our noses for millennia. Let us then introduce Zealandia.
The eleven-strong research team behind the study argue that New Zealand and New Caledonia are not just an island chain. Their labors seem to show that they are, actually, part of a single 4.9 million square kilometer slab of virgin continental crust distinctly separate from Australia.
The idea is nothing new. Bruce Luyendyk of the University of California coined the phrase in the 90s. As flattering as this is, Bruce never meant for it to define a new continent. The area in question is a collection of continental crust in and around New Zealand to the East of Australia. "The reason I came up with this term is out of convenience," Luyendyk says. "They're pieces of the same thing when you look at Gondwana. So I thought, 'why do you keep naming this collection of pieces as different things?"
Pieces of the same jigsaw
This kind of assortment of "pieces" of continental crust are usually termed microcontinents and this region of the world is no exception. The difference is that now a collection of more evidence seems to point to a larger, more cohesive and "continent looking" piece of the Earth's crust.
The new study used recent and detailed satellite-based elevation and gravity maps. They looked at the ancient seafloor which shows that Zealandia is indeed part of one unified region. This potentially overturns centuries of assumptions that they are merely an island chain. The data also seems to show that the area might be as big as the area of greater India. Certainly larger than Madagascar, New Guinea, Greenland and other microcontinents around the world.
The paper states that "If the elevation of Earth's solid surface had first been mapped in the same way as those of Mars and Venus (which lack […] opaque liquid oceans).". They continue "We contend that Zealandia would, much earlier, have been investigated and identified as one of Earth's continents."
[Image Source: GSA Today]
Close, but no cigar
Just like India, Zealandia is certainly big enough to be termed a continent. The newly proposed continent, unlike India, is still separate from other land masses. Well, for now, it hasn't yet collided with Australia. Cato Trough separates the two by around 25 kilometers and closing.
Its definition is a little tricky, however. Zealandia is split in two by the Austrailian and Pacific plates, unfortunately. This would seem to suggest it as being a collection of segments rather than a unified continent. This is not a deal breaker, no pun intended. Similar boundaries marble other continents too. Good examples include Arabia, India and Central America. California, for instance, has a massive plate boundary running straight through it.
Rock samples and satellite imagery also seem to confirm that Zealandia is part of a unified slab as well. Today only around 5 percent of it is visible as the Islands of New Zealand and New Caledonia. The constant waltz of plate tectonics has stretched and thinned the continent. This interplay over millions of years has resulted in most of it being submerged in modern times.
All hail Zealandia
"The scientific value of classifying Zealandia as a continent is much more than just an extra name on a list," the study team notes. "That a continent can be so submerged yet unfragmented makes it a useful and thought-provoking geodynamic end member in exploring the cohesion and breakup of continental crust."
Luyendyk agrees with the team and believes the distinction of Zealandia as a continent won't end up as a scientific curiosity. It may open up the pandora's box of larger consequences for the society.
"The economic implications are clear and come into play: What's part of New Zealand and what's not part of New Zealand?" he says.
Current United Nations agreements actually make mention of continental shelves as boundaries that determine where resources can be extracted. This could prove highly lucrative for New Zealand. They may have tens of billions of dollars' worth of fossil fuels and minerals lurking off its shores. That's a nice present for them to unwrap.