Africa, America, Asia, Europe, Oceania… Five continents. This is what appears in geography textbooks. Ah yes, but we forget Antarctica! And then is it America or the Americas? And Oceania? A global entity or several land masses? And Europe and Asia aren't really separate, so it's Eurasia…one continent!
In short, how many continents are there really? This question visibly torments the Sciences du journalist. New York Times, Matt Kaplan, who gives the possible answers in a fascinating column published this week. Because yes, there are several answers.
Are we talking about geography or geology? Geopolitics or history? All these points of view, he recalls, condition the very definition of a continent.
And if we start from a geological point of view, there are four conditions to be met to be a “real” continent:
A high altitude relative to the ocean floor. A wide variety of silica-rich igneous, metamorphic and sedimentary rocks. A crust thicker than the surrounding oceanic crust. Well-defined boundaries around a sufficiently large area.
But the whole question, reminds the journalist, is to know what is big enough. “Anything big enough to change the map of the world is important”responds in the New York Times Nick Mortimer, geologist at the GNS Science Institute in New Zealand.
“Antarctica and everything in between”
Okay, so what about the very volcanic Iceland, located atop a fault that extends around the Earth, the Atlantic branch of the Mid-Ocean Ridge, which rises above sea level at this point? the sea ? The island is spreading lava composed of molten continental crust beneath the seas surrounding it, according to a recent study published in Geology by the team of Valentin Rime, geologist from the University of Fribourg, in Switzerland.
And what about the ridge in the Red Sea that separates Africa from Asia? “at the speed at which nails grow” . “At this location there is no obvious point where Africa ends and Asia begins”recalls the journalist. And finally, in which category should New Zealand be classified, which is not on the same continent as Australia, geologically speaking? It could stand alone, and constitute part of its own continent, Zealandia, some scientists suggest. We would therefore be at nine continents.
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