In elementary school we're taught that there are seven continents. But there are actually many geologists that think there should be eight. Their proposed eighth continent, named Zealandia, is about 95 percent submerged, but that doesn't mean it shouldn't qualify as a continent.
Where is Zealandia?
Wikimedia//Ulrich Lange, Bochum, Germany
According to this article published by the Geological Society of America, Zealandia is located west of Australia. This map, created by the article's authors, shows Zealandia in gray. The islands of New Zealand are part of Zealandia, but most of the rest of the continent is underwater.
How can it be a continent if it's mostly underwater?
There is no actual requirement that a continent must be composed of dry land. According to the Glossary of Geology, a continent is "one of the Earth's major land masses, including both dry land and continental shelves." According to the article, the geologic community generally agrees that continents have the following four attributes:
1. High elevation compared to areas floored by oceanic crust
For most of us who aren't sure that that means, this diagram shows the difference between oceanic crust and continental crust.
2. A broad range of siliceous igneous, metamorphic and sedimentary rocks
Remember in eighth grade when you learned about all the different types of rocks? This is basically just saying that a continent has to have all of them.
3. Thicker crust and lower seismic velocity structure than oceanic crustal regions
Seismic velocity is the rate at which a seismic wave (caused by an earthquake) travels through continental crust or oceanic crust. A continent will have lower seismic velocity (the waves will travel slower) in comparison to oceanic crust regions.
4. Well-defined limits around a large-enough area to be considered a continent rather than a microcontinent or continental fragment
The authors argue that Zealandia satisfies all four of these criteria. Even though most of the area is submerged, the submerged regions are still far more similar to continental crust than to oceanic crust.
The paper makes a good case (if you can understand all the scientific jargon), but whether the rest of the geological community will get on board is tough to say.