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Saturday, January 16, 2021

Zealandia: The Sunken Continent

How many continents does the Earth have? Easy question it is, but it may be a bit complicated.

Some will say seven, South America, North America, Europe, Africa, Asia, Australia, and Antarctica. Others will say six, America, Europe, Africa, Asia, Australia, and Antarctica. A person who knows a whole heap about geography will say that nothing divides Europe and Asia, so there will only be five continents, America, Eurasia, Africa, Australia, and Antarctica. And before Suez Canal was dug by Suez Canal Company between 1859-1869 and officially open on November 17, 1869, Africa and Eurasia were connected by land.


Having this said, there are only four continents, America, Afro-Eurasia, Australia, and Antarctica. But still, some would argue about it and will say that there is still one more continent, the 8th continent, Zealandia.

“If we could pull the plug on the world’s oceans, it would be quite clear to everybody that we have mountain chains and the big high-standing continent”, said Nick Mortimer, a geologist at GSN Science in Dunedin, New Zealand and co-author of the study “Zealandia: Earth’s Hidden Continent”.

Also known as Te Riu-a-Māui or Tasmantis, Zealandia is almost an entirely submerged mass of continental crust, igneous, sedimentary layer metamorphic rocks, which form geological continents, not an oceanic crust. It receded after breaking away from Gondwanaland, a supercontinent that existed from the Neoproterozoic until the Jurassic 79-83 million years ago. It was also described as a continental fragment, a microcontinent, a submerged continent, and a continent.

The name Zealandia was proposed in the year 1995 by Bruce Luyendyk, an American geophysicist and oceanographer. Unlike the Lost City of Atlantis that vanished in just one night, Zealandia took about 23 million years to be submerged its 94% landmass in the Pacific Ocean. Having New Zealand as the largest part (267,988 km2 (103,471 sq. mi, or 93%) of it above sea level followed by New Caledonia (18,576 km2 (7,172 sq. mi or 7%), and the remainder is made up of territories of Australia, with a total area of 286,655 km2 (110,678 sq. mi) making it the largest microcontinent in the world.

Its size is more than twice the size of the second-largest microcontinent, and more than half of the Australian continent separated from Cato trough. But because of some geological considerations, like crustal thickness and density, it became arguably a continent on its right. 

Image: Geology In
Image: TRT World

This argument paved the way for the geologist to make a further study for Zealandia to claim its rightful title, the 8th continent. But what are the criteria to be called as continent? In their study entitled “Zealandia: Earth’s Hidden Continent” Nick Mortimer’s team cited some measures on how to qualify to be a continent. A continent must have and elevation above that of the ocean surrounding it. Looking from an ocean floor elevation map of the Earth, Zealandia’s shape rises over a kilometer over the surrounding seas. The crust of the continent must contain a wide range of igneous, sedimentary, and metamorphic rocks. This principle can be supported by the rock samples taken from the sunken continent that revealed rock types variation.

The crust must be thicker and less dense than oceanic crust and therefore have a lower seismic velocity. Zealandia may be thinner than the other continents. It is also noticeably more viscous than the oceanic crust or the uppermost layer of the oceanic portion of the tectonic plate. It is also lesser in dense than oceanic crust.

A well-defined extent that is large enough to constitute a continent rather than a microcontinent or continental fragment. Australian Continent’s size is 7,692,024 km2 making it the smallest official continent; therefore, a more significant landmass can be in the running to be a continent. Then the largest island measures 2, 166, 000 km2, which is Greenland, in which any smaller landform cannot be qualify to be a continent rather and island. Zealandia is over twice the most extensive island’s size and over half more prominent than the smallest continent.

So what does it needs to be called a continent? Some will say that it needs to have a massive expanse of land in which Zealandia has very little. But proponents of the argument to whether Zealandia is a continent or not suggested that if the study will be conducted to Earth and its continent like the way research on other planet is directed, disregarding surface liquid. Zealandia’s status as a bonafide continent would become apparent because it is higher than its surrounding crust.

But what makes a continent, a continent? How many continents Earth have? 

Further study needs to be done along with thorough investigation, and with the advent of technology, geologists will soon come up with the right affirmation.

“If it wasn’t for the ocean, it would have been recognized as such long ago.”-Nick Mortimer
By Kris De Vera Estrella, IFY Books

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