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Global map, showing continents and ocean basins

When we look at the globe, or at a map of the world, we can't help being impressed by the vastness of the large oceans: the Pacific, Atlantic, and Indian Oceans, even the Arctic Ocean.
Airplanes take long hours crossing them, ships several days and sometimes weeks. Oceans seem to tell us they have been there forever, mighty, powerful, and permanent.

They are all of that -- or almost. They are quite young, measured in geological time. By and large, they are not older than 180 million years (Ma); which, of course, is quite old, but not compared to the age of the continent we are living on, which had its beginnings more than 20 times farther back in time.

So, where do oceans go when they grow old? Good question! We shall know more about this after the slide show is over. Most of us will be surprised to hear that in many parts of our country -- where today we grow grains, raise livestock, and mine resources -- an old ocean once may have been, dotted by beautiful islands, small and big. Or, a majestic mountain chain, which would have blocked our view, may have towered there had we been around that early in Earth's life.

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