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These United States: A Chip Off a Very Old Block: Discovering Pangaea, the Real Motherland! 

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pangaea
Caption
Have you ever looked at a map or a globe and noticed that the coasts of South America and Africa would fit together almost perfectly if you could slide them next to each other? It almost seems like they're two puzzle pieces that would snap in place if only the South Atlantic Ocean weren't in the way.

Coincidence...or something more?

Something more! And not only is there a link between South America and Africa, but the shapes of all seven continents are linked too. Geologists are just beginning to understand the processes that shape our world, but people have wondered about these strangely related shapes for as long as we humans have been drawing maps.

A Dutch cartographer, or mapmaker, named Abraham Ortelius suspected in 1596 that the continents were ripped, piece by piece, from one large land mass by huge floods and earthquakes. People in the 1700s believed that the great flood written about in the Bible carved the earth's mountains and coastlines. And in 1785, a Scottish geologist named James Hutton introduced "uniformitarianism," the idea that the forces at work on the planet now are the same forces that have been at work for ages.

Map
The term "continental drift" showed up in 1912, when one Alfred Lothar Wegener proposed that, around 220 million years ago, there were no continents, only one huge land mass that he called "Pangaea," or "all lands" in Greek. Wegener thought that Pangaea split into two parts -- a northern part and a southern part -- about 200 million years ago, and that those halves eventually split again and drifted to where our continents are now.

But what kind of force is strong enough to move entire continents thousands of miles across the ocean?

We still aren't sure, exactly, but scientists began finding solid evidence in the 1950s leading to the "theory of plate tectonics." This theory claims that the continents and oceans are floating on a hardened crust which lies over a thick layer of hot iron- and magnesium-bearing rock called the mantle. The mantle extends down at least 1,800 miles and is very hot -- a blistering 4,000 C (7,200 F) at its core -- from the birth of the planet and the heat generated by the compression it experiences from gravity.

Away from the center of the earth, though, there isn't enough pressure to solidify the mantle, and it melts into a thin layer of thick, gel-like "magma" which covers the solid mantle in a layer called the "asthenosphere." The top of the asthenosphere has cooled into the solid crust that we live on, but has been broken into gigantic pieces that are forced into and over one another by currents in the ooze underneath. These pieces of floating land are called "tectonic plates," and their movement around the Earth's surface is how Pangaea was split apart and how its pieces got to their current locations!

What's more, the oozing currents beneath the shifting tectonic plates are like the currents in a pot of boiling water: they rise and fall in what look like little teams of bubbles. The rising bubbles carry the hot magma up to where it touches the bottom the crusty level and starts to melt away parts of it until a weak spot forms. When that happens, the hot magma breaks through the crust, cools down and hardens into new crust.

The falling bubbles carry the magma down toward Earth's core, sometimes melting and pulling the edges of two tectonic plates with them, causing one plate to rise above the other. When this happens -- and it happens on a huge scale over a long period of time -- the top plate may rise upward into tall, jagged mountain ranges such as the Himalayas. Another possibility is the creation of volcanos.

So there you have it. Just when you thought you were going to learn about the history of the United States of America, you're really learning about a chip off a (very) old block called Pangaea. We've literally come a very long way over 220 million years!

The Team

 

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