Is Zealandia a continent? | Science News for Students

Is Zealandia a continent?

Landmass lies mostly beneath the Pacific Ocean
Mar 13, 2017 — 7:10 am EST
New Zealand

New Zealand rises from the center of a previously unknown, largely submerged continent, scientists propose. They call it Zealandia.

Stuart Rankin/Flickr (CC BY-NC 2.0), NASA

Lurking beneath New Zealand is a long-hidden continent, geologists now propose. They call it Zealandia. Don’t expect it to soon end up on a map on your classroom wall, though. Nobody is in charge of officially designating a new continent. Scientists will have to judge for themselves if Zealandia should be added to the ranks of continents.

A team of geologists pitched the scientific case for judging this a new continent in the March/April issue of GSA Today. Zealandia is a continuous expanse of continental crust. It covers some 4.9 million square kilometers (1.9 million square miles). That’s about the size of the Indian subcontinent. But it would be the smallest of the world’s continents. And unlike the others, around 94 percent of Zealandia hides beneath the ocean. Only New Zealand, New Caledonia and a few small islands peek above the waves over it.

“If we could pull the plug on the world’s oceans, it would be quite clear that Zealandia stands out,” says study coauthor Nick Mortimer. He is a geologist at GNS Science in Dunedin, New Zealand. Zealandia rises about 3,000 meters (9,800 feet) above the surrounding ocean crust, he notes. “If it wasn’t for the ocean level,” he says, “long ago we’d have recognized Zealandia for what it was — a continent.”

Story continues below map

continents map
A landmass called Zealandia (gray region) deserves to join the ranks of continents, some geologists now propose. Only 4 percent of Zealandia rises above sea level (dark gray), including New Zealand. But swaths of other continents also are submerged along their margins (light-shaded regions).
Nick Mortimer/GNS Science

This landmass, directly east of Australia, will face an uphill battle for continent status. New planets and slices of geologic time have international panels that can officially name them. But there is no such group to officially validate new continents. The current number of continents is already vague. Most everyone agrees on five of them: Africa, Antarctica, Australia and North and South America. Some people, however, combine the last two — Europe and Asia — into one huge Eurasia. There’s no formal way to add Zealandia to this mix. Proponents will just have to start using the term and hope it catches on, Mortimer says.

This odd path forward stems from the simple fact that nobody expected another continent would ever need to be added, says Keith Klepeis. He is a structural geologist at the University of Vermont in Burlington. He supports the move to add Zealandia. Its discovery illustrates that “the large and obvious can be overlooked in science,” he says.

A case for a new continent

Earth is composed of three main layers — a core, mantle and crust. The crust comes in two types. Continental crust is made of rocks such as granite. A much denser ocean crust is made of a volcanic rock known as basalt. Because ocean crust is thinner than continental crust, it doesn’t rise up as far. That has created low spots around the globe that have been filled in by oceans.

Continents can’t be made of oceanic crust. But having continental crust isn’t enough to confirm Zealandia is a new continent. For a decade, Mortimer and others have been building a case that it is. They have now ticked off all of the boxes that they believe are required. For instance, the region is composed of continental rocks such as granite. The region also is distinct from nearby Australia. (That is thanks to an intervening stretch of ocean crust.)

“If Zealandia was physically attached to Australia, then the big news story here wouldn’t be that there’s a new continent on planet Earth,” Mortimer says. “It’d be that the Australian continent is 4.9 million square kilometers larger.”

There are other geologic features that rise from the seafloor. These can include volcano-built submarine plateaus. But they either are not made of continental crust or are not distinct from nearby continents. (That's an argument for why Greenland would not be a continent).

Zealandia map
The proposed continent of Zealandia (outlined in red) covers roughly 4.9 million square kilometers (1.9 million square miles) east of Australia. Most of its territory hides below the Pacific Ocean. Only a few of its areas, such as New Zealand, rise above its waves.
N. Mortimer/GNS Science

Size might prove a sticking point, however. No minimum size requirement exists for continents. (Both submerged and dry areas contribute to a continent’s overall size.) Mortimer and his colleagues propose a 1-million-square-kilometer (0.4-million-square-mile) minimum. If this lower size limit is accepted, Zealandia would become the scrawniest continent by far. It is just a little more than three-fifths the size of Australia.

Scientists dub smaller fragments of continental crust as “microcontinents.” Those that are attached to larger continents are subcontinents. Madagascar is one of the larger microcontinents. Zealandia is about six times larger. That means it fits better as a continent than a microcontinent, Mortimer and his colleagues maintain.

“Zealandia’s in this sort of gray zone,” says Richard Ernst. He is a geologist at Carleton University in Ottawa, Canada. He proposes that an intermediate term could help bridge the gap between microcontinent and full-blown continent. He suggests that it be called a mini-continent. That definition would cover Zealandia. It also would cover other not-quite-continents such as India before it plowed into Eurasia tens of millions of years ago. Such a solution would be similar to the route taken for Pluto. It was demoted from planet to the newly coined “dwarf planet” status in 2006.

Scientists previously assumed that New Zealand and its neighbors were an assortment of islands — fragments of long-gone continents and other geologic odds and ends. Recognizing Zealandia as a coherent continent would help scientists piece together ancient supercontinents, Mortimer says. It also could aid in the study of how geologic forces reshape landmasses over time.

Zealandia probably began as part of the southeastern edge of the supercontinent Gondwana before it began peeling off around 100 million years ago. This breakup stretched, thinned and distorted Zealandia, which ultimately lowered the region below sea level.

Power Words

(more about Power Words)

Antarctica     A continent mostly covered in ice, which sits in the southernmost part of the world.

basalt       A type of black volcanic rock that tends to be very dense (unless volcanic eruptions seeded it with lots of air pockets). 

coauthor     One of a group (two or more people) who together had prepared a written work, such as a book, report or research paper. Not all coauthors may have contributed equally.

colleague     Someone who works with another; a co-worker or team member.

continent     (in geology) The huge land masses that sit upon tectonic plates. In modern times, there are six geologic continents: North America, South America, Eurasia, Africa, Australia and Antarctica.

continental crust      (in geology) Rock that underlies most of Earth’s continents. It is less dense than ocean crust and sort of floats above ocean crust in regions where the two may meet and collide. This material is typically formed of rocks such as granite.

core     In geology, Earth’s innermost layer. 

crust     (in geology) Earth’s outermost surface, usually made from dense, solid rock.

dwarf planet     One of the solar system’s small celestial objects. Like a true planet, it orbits the sun. However, dwarf planets are too small to qualify as true planets. Prime examples of these objects: Pluto and Ceres.

Eurasia     That part of the globe covered by Europe and Asia.

geologic      An adjective that describe things related to Earth’s physical structure and substance, its history and the processes that act on it. People who work in this field are known as geologists.

Gondwana     One of Earth’s two supercontinents that existed during the Devonian Period, which ran from roughly 416 million years ago to 360 million years ago. It’s when some of the earliest plants emerged, initially with no leaves or roots. By the end of this period, ferns and seed plants had evolved. Some shellfish and trilobites shared the oceans with various fishes. And many wingless arthropods (ancestors to spiders and insects) colonized the land.

granite     A type of hard igneous rock, which contains coarse-grained inclusions (essentially mini rocks within a rock) of various minerals, chiefly quartz, feldspar and mica.

Greenland     The world’s largest island, Greenland sits between the Arctic Ocean and North Atlantic. Although it is technically apart of North America, just east of Northern Canada, Greenland has been politically more linked to Europe. Indeed, Vikings arrived in Greenland around the 10th century, and for a time the island was a colony of Denmark. In June 2009, Greenland became an independent nation. Ice covers roughly 80 percent of Greenland. Indeed, the Greenland ice sheet is the world’s largest. If its frozen water were to melt, it could raise sea levels around the world by 6 meters (about 20 feet). Although this is the 12th biggest nation (based on surface area), it averages the fewest people per square kilometer of its surface area.

intervene      To come in between.

landmass     A continent, large island or other continuous body of land.

mantle     (in geology) The thick layer of the Earth beneath its outer crust. The mantle is semi-solid and generally divided into an upper and lower mantle.

New Zealand     An island nation in the southwest Pacific Ocean, roughly 1,500 kilometers (some 900 miles) east of Australia. Its “mainland” — consisting of a North and South Island — is quite volcanically active. In addition, the country includes many far smaller offshore islands.

ocean crust     Rock that makes up much of the surface below the oceans. It is very dense and tends to sort of sink down when it meets and collides with continental crust. Ocean crust typically is made of basalt, a type of volcanic rock.

planet     A celestial object that orbits a star, is big enough for gravity to have squashed it into a roundish ball and has cleared other objects out of the way in its orbital neighborhood. To accomplish the third feat, the object must be big enough to have pulled neighboring objects into the planet itself or to have slung them around the planet and off into outer space. Astronomers of the International Astronomical Union (IAU) created this three-part scientific definition of a planet in August 2006 to determine Pluto’s status. Based on that definition, IAU ruled that Pluto did not qualify. The solar system now includes eight planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.

plateau       A flat area of land, high above sea level. It’s sometimes referred to as “tableland.” Several of its edges tend to be steeply sloped (cliffs).

Pluto     A dwarf planet that is located in the Kuiper Belt, just beyond Neptune. Pluto is the tenth largest object orbiting the sun.

submarine        A term for beneath the oceans. (in transportation) A ship designed to move through the oceans, totally submerged.

volcano     A place on Earth’s crust that opens, allowing magma and gases to spew out from underground reservoirs of molten material. 

Zealandia      The name for a proposed new continent that sits largely submerged beneath the ocean. If confirmed, it would be the smallest continent. The only easily visible parts of it are New Zealand and New Caledonia. These islands rise east of Australia in the Southern Hemisphere.


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Journal:​ ​​ N. Mortimer et al. Zealandia: Earth’s hidden continent. GSA Today. Vol. 27, March/April 2017. doi: 10.1130/GSATG321A.1.