We’ve all learned in school there are 7 continents: Asia, Africa, Antarctica, Australia, Europe, North America and South America. One would imagine that a continent is not easily missed or something that appears overnight, so it may come as a surprise to find out that, in 2017, a team of geologists discovered there is an 8th continent on our planet: Zealandia.
In the times of explorers, Dutch sailor Abel Tasman was determined to find Terra Australis, what at the time was believed to be large landmass somewhere in the Southern Hemisphere that had to exist to balance out Europe. On 14 August 1642, he started heading south from his company’s base in Jakarta, eventually reaching the South Island of New Zealand. Although hostile interactions with the native Māori people made him return without ever setting foot on land, he was content with his discovery.
Two centuries later, in 1895, Scottish naturalist Sir James Hector first documented signs of a continent, writing about New Zealand as “the remnant of a mountain-chain that formed the crest of a great continental area that stretched far to the south and east, and which is now submerged”.
Another century later, in the 1960s, geologists first agreed on what actually constitutes a continent, defining 4 characteristics that a landmass needs to have to be classified as such:
- Elevation – The landmass, whether dry or submerged beneath the ocean, should be elevated above the surrounding ocean crust.
- Geology – The landmass should contain different types of rock: igneous, metamorphic, and sedimentary.
- Crustal structure – The landmass should consist of the continental crust, which is thicker and has a lower seismic velocity than the oceanic crust.
- Limits and area – The landmass should have clearly-defined boundaries and an area of more than one million square kilometres.
Still, no further advancements were made regarding the south continent for another several decades. In 1994, the United Nations adopted the Convention on the Law of the Sea, allowing states to claim 200 nautical miles from the shore as legal territory, having exclusive access to any mineral riches or oil found in that area. “If New Zealand could prove that it was part of a larger continent, it could increase its territory by six times. Suddenly there was an abundance of funding for trips to survey the area, and the evidence gradually built up”, the BBC writes.
Satellite images showing the variations in the Earth’s gravity across the seafloor were then able to clearly reveal Zealandia as a misshapen mass almost as large as Australia.
2. Characteristics and formation
After a series of analyses of the seafloor, geologists firmly concluded in 2017 that, despite most of Zealandia being submerged under water, it fulfilled all the characteristics of being classified as a continent. Like all other continents, Zealandia has high elevation compared with surrounding oceanic crust, it consist of relatively thick and low-velocity continental crust, comprising rocks such as granite, schist and greywacke, and, with an area of 5 million km2, is large enough.
Present day Zealandia broke off from the southern supercontinent of Gondwana. Gondwana started to gradually break up about 150 million years ago, with India and Africa drifting north. About 100 million years ago, the Zealandia part of the Gondwana crust started to stretch, eventually breaking off as its own continental piece, and oceanic crust formed to fill the gap between Zealandia and the still-joined Antarctica and Australia.
With time, Zealandia moved north and sank under the ocean with land area getting smaller as the advancing seas carved a flat marine surface across most of the continent. About 25 million years ago however, the Pacific-Australian Plate boundary cut Zealandia in half, then mountains and volcanoes formed again and land area increased. Today, most of Zealandia sits hidden underwater, with only the islands of New Zealand and New Caledonia visible above the ocean surface.
In 2018 New Zealand’s Institute of Geological and Nuclear Sciences (GNS Science), which spends about $7M a year on basic underpinning research into the geology and geophysics of Zealandia, asked respected Auckland University academic, Associate Professor Mānuka Hēnare, to research and recommend a Māori name that reflected the nature and position of the continent. Thus, the dual name of Te Riu-a-Māui / Zealandia was agreed on. Te Riu-a-Māui literally means the hills, valleys and plains of Māui – the great East Polynesian ancestor who sailed and explored the great ocean. According to legend, Māui caught a giant fish and pulled it out of the ocean, the fish becoming the islands of New Zealand.