In elementary school, we learn the basic indisputable facts of life. Two plus two is four. The world is round. There are seven continents on Earth.
Pretty basic stuff, right? Only the latter isn’t quite as straightforward as our first-year teachers led us to believe.
In the United States, students learn that there are seven continents: North America, South America, Europe, Asia, Africa, Australia, and Antarctica. And by that standard, continents make up the vast majority of the planet’s land surface, roughly 57 million square miles (148 million square kilometers).
But this is not the last word on the matter. For example, in Europe, students usually learn that there are really only six continents: Africa, America, Antarctica, Asia, Australia/Oceania and Europe. There’s even a five-continent model, which lists Africa, Europe, Asia, America, and Oceania/Australia. (That’s why there are five rings on the Olympic flag.) And some experts believe four is the way to go, using landmasses as criteria. naturally separated by water rather than artificial channels (AfroEurasia, America, Antarctica and Australia).
Heck, as recently as the 1800s some people say there were only two continents, the Old – comprising Europe, Africa and Asia – and the New, which encompassed the North and South America.
It doesn’t take much imagination to figure out why it’s more complicated than it looks. Even as a child, you might have wondered how anyone would view Asia and Europe as different continents when they are welded together into huge tracts of land.
Let’s try to simplify.
What makes a continent a continent?
Traditionally, we have learned that continents are huge landmasses with clearly defined borders separated by oceans.
According to a 2017 article published in the journal of the Geological Society of America, GSA Today, “The ‘Glossary of Geology’ defines a continent as ‘one of Earth’s major landmasses, comprising both arid lands and continental shelves”. It is generally accepted that continents have all of the following attributes: (1) high elevation relative to regions covered by oceanic crust; (2) a wide range of igneous, metamorphic, and sedimentary siliceous rocks; (3 ) thicker crust and lower seismic velocity structure than regions of oceanic crust; and (4) well-defined boundaries around an area large enough to be considered a continent rather than a microcontinent or fragment continental… As far as we know, the last point – how big a piece of continental crust must be to be called a continent – is almost never discussed.”
“Nothing, really, determines a continent except historical convention,” Dan Montello, a geography professor at the University of California, Santa Barbara, says via email. “A bit of a stretch but mostly valid. Certain factors make a landmass more or less likely to be called a continent at various times in history, by various people, but nothing can be said to determine the continentality of a totally principled and non-arbitrary way.”
Take for example the vast country of Russia, 6.6 million square miles (17 million square kilometers). Why is it part of Europe rather than Asia? “The Ural Mountains are taken to separate Asia and Europe, but only because the Russians wanted their great city of Moscow to be European, so the Urals was a convenient marker for this arbitrary decision” , explains Montello.
“Continents are (for the most part) spatially contiguous collections of landmasses larger than countries but smaller than hemispheres; of course, continents do not necessarily fit entirely within single terrestrial hemispheres (and, therefore , cannot be defined by latitude or longitude ranges).”
What about plate tectonics? If some landmasses are constrained to one of these massive moving masses, can we safely call it a continent? Montello says no.
“Plate tectonics has nothing to do with it historically, and it certainly could not provide a principled basis for continents now; nearly all continents include parts of multiple plates, and continental boundaries are not, and never were, defined by plate boundaries.”
The same goes for the climate. After all, the continents contain multiple climates, as evidenced by the arctic cold of Alaska versus the humid heat of Florida, and they are both part of North America. Mountain ranges and continental shelves aren’t helpful either, he says. The coastline is useless.
What about cultural ties or politics?
“Neither ethnicity, nor race, nor culture, nor politics have ever defined the continents, except by largely mythical conventional theories, such as ancient and fallacious ideas about the correspondences between races and continents” , he said. “Politically, Hawaii is part of the United States but is in Oceania rather than North America; Greenland is controlled by Denmark (for now) but is considered part of the North American continent.
Really, it can come down to who – and when – you ask.
“No one can say in principle how many continents there are, because decisions are largely based on convention, and convention that passes and goes out of fashion over time, and is still debated today,” Montello says.
He concedes that nowadays many geographers would opt for a list of seven continents: Africa, Antarctica, Asia, Europe, North America, Oceania and South America. But it is equally certain that some of them would combine Asia and Europe into Eurasia, identify Oceania in other ways, or combine North and South America into the Americas.
“There is simply no ‘Czar’ or ‘CEO’ of continents or any other ultimate authority, so it is pretentious for anyone to claim to have the authoritative answer,” Montello says.
But don’t worry, if you can’t handle that kind of definition, everything changes. The continents drift at a rate of about one inch (2.5 centimeters) per year.
Originally published: June 22, 2020