Why do most continents look like southward-pointing triangles?

http://www.theguardian.com/lifeandstyle/2015/mar/04/continents-south-triangles

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Why do most continents look like triangles, coming to a point at their southern end, not the northern? I pondered this while looking at a map of the world, that looked like jagged triangles all pointing to the south pole.

Lena Isayev, Exeter, Devon

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