Theory and Evidence of Continental Drift

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  • 0:01 A Supercontinent
  • 0:47 Submarine Science
  • 1:51 Seafloor Spreading
  • 3:00 Alfred Wegener's Puzzle
  • 3:45 More Evidence
  • 4:21 Lesson Summary
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Lesson Transcript
Instructor: Kevin Newton

Kevin has edited encyclopedias, taught middle and high school history, and has a master's degree in Islamic law.

If you've ever flown to Europe, you know that it's a long flight. However, if the theory of continental drift has anything to say about it, that flight is only going to get longer. That's right - we are drifting away from Europe!

A Supercontinent

Look at a map of the world. As long as we can remember, it's looked pretty similar to the way it looks now. North America is to the north and west of South America, and both are separated from Eurasia, Africa, and Australia by large oceans. However, this was not always the case. Millions of years ago, there was only one continent, Pangaea. You'll sometimes see it spelled without the middle 'a,' as Pangea, but both describe the large supercontinent that used to make up the vast majority of the land on our planet. Sounds kind of far-fetched, doesn't it? In this lesson, we're going to prove the idea of continental drift, the idea that the continents are moving, and see how it was that this was figured out.

Submarine Science

Chances are you know what a submarine is. While the technology has been around since the American Revolution, it was only in the 20th century that the technology really took off. During both World Wars, the Germans used their U-Boats to wreck trans-Atlantic shipping, and the Americans used similar submarines in the Pacific during World War II. However, these submarines were really more like boats that could submerge to attack. True submarines, which could stay submerged for weeks and months at a time, came later, during the Cold War.

These vessels were capable of going much deeper than earlier boats, which meant that there was a real need for better charts of the topography of the ocean floor. Naval submarines quickly went to work charting the depths on missions directed by the Office of Naval Research. Even today, much of the most detailed aspects of this knowledge remain a classified secret. Only people with Top Secret clearance at intelligence agencies and the Office of Naval Research have access to the most comprehensive charts.

Seafloor Spreading

Still, there were some things that the navies of the United States, Soviet Union, and United Kingdom could not explain, so they turned to science. One of the most enigmatic of these was the mid-Atlantic ridge. The mid-Atlantic ridge is located in the middle of the Atlantic ocean, and it is where the seafloor is 2-3 km higher than the rest of the ocean floor. Later, scientists would discover that the ridge was actually part of the ocean ridge system, which runs through the middle of many oceans and is more than 80,000 kilometers long.

It looks like the two sides of the ocean floor were sewn together, with a valley in between two high ridges. Even more interesting, the rock at the top of this ridge is much younger than the rest of the ocean floor. Further study proved that the seafloor was spreading, and the new rock was coming from the earth's magma. In other words, the Atlantic Ocean is getting wider. This idea that the seafloor was expanding is referred to as seafloor spreading. The person who finally figured this out was American Rear Admiral Harry Hess, and he did so during the 1960s.

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