The world is split up into continents, there are seven in all.

And if you get the gist, we’re going to make a list,

From biggest to small …

Your kids may have come home from school singing this infectious ditty, or another like it. But are there really seven continents?

Anyone with a map can see that Asia and Europe are connected. They are often called Eurasia for that reason. The divide is pretty arbitrary, more culturally than scientifically defined. So, is it fair to say that there are actually only six continents?

That is just the first slippery step on a well-oiled slope. What about North America and Asia?

They are connected by the Bering Sea Shelf, once dry land crossed by humans and flooded only in the geologically recent past. Technically speaking, that makes Asia, North America and Europe all one continent. Does that mean there are only five?

Other experts contend that five, six and seven are wrong and argue in favor of eight continents. There are even those who go as far as to say there are only two.

Hiding within the simplicity of the song, there is an illusion of general agreement about the number of continents.

The dispute arises in part because there are really two types of continents: Those recognized by cultures around the world, and those recognized by geologists. Cultures can define a continent any way they want, while geologists have to use a definition. And geological research in recent years has made defining continental boundaries less simple than it might have once seemed as researchers find evidence of unexpected continental material.

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