Plate+Tectonics

Plate Tectonics
Let's start off with a little song...the Alfred Wegener Song!

Imagine that it is springtime and you are crossing a frozen lake. As you start out, the ice seems stable and solid, but in fact, it is not. Before you reach the other shore, the ice starts to break up. Large cracks develop, separating the ice into huge plates that are moved by wind and currents in the water below. Some of these ice plates are pulled apart, while others are smashed together forcing one to ride up over the other. Some of the plates drift away to form floating platforms.

 What does this have to do with the study of geology? The earth's structure is similar to a frozen lake. The surface of the earth is a thin layer of moving plates, and below these plates is material that is also in motion. Every year around the world, there are about 30 000 earthquakes that are strong enough to be felt. These earthquakes indicate the movement of parts of the earth's rigid upper layer.

 Seismologists are scientists who study earthquakes. They have discovered that most earthquakes occur only in a few areas. Earthquakes frequently occur where the edges of the earth's plates are moving in relation to each other. Not all seismologists, however, agree on the exact locations of some of the boundaries.

Questions
1. Try to think of another example of what you could liken the earths crust to. Record it! 2. Where do most earthquakes take place? Why? 3. Do we have many earth quakes here in Brantford? Why do you think that?

 PLATE TECTONICS
 If you examine a map of the world, you might notice that the shapes of South America and Africa look like they could fit together. If they were once together, why are they now apart, and what forces could move such large land masses?

 In 1915, Alfred Wegener, a German scientist, said that the only possible answer was continental drift. He suggested that about 300 million years ago all of the earth's land masses, which were in constant motion, collided to form one super-continent. He called it Pangaea, which means "all land". About 200 million years ago, the super-continent of Pangaea started to break up. The pieces drifted in different directions to their present positions.

Wegener's theory of continental drift stated that only continents drifted. Today, we know that plates are much larger than continents and contain both continental and oceanic trust.

 What proof did Wegener have that the huge continents of the earth could move and that his theory of continental drift was correct? Most scientists disagreed with Wegener because he could not explain what mechanism was powerful enough to move huge continents. It was not until the 1960s that the technology existed to further develop Wegener's theory. In fact, it was a Canadian, J. Tuzo Wilson, who helped to spark new interest in the theory of continental drift. By 1968 a new theory, known as plate tectonics, was developed.

theory: an explanation based on observation and reasoning

 tectonics: relating to the internal forces which deform the earth's crust

<span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 150%;"> Plate tectonics is the theory that helps explain most geologic processes. The theory states that the earth's outer shell is made up of about twenty plates. Most of these plates are made up of both a continent and an ocean. They are moving over a weak layer of hot rock, several hundred kilometers below the earth's surface, which flows like slow-moving plastic. No one fully understands the forces that cause the plates to move over this weak layer. It is possible that the unequal distribution of heat within the earth causes convection currents to move the plates.

<span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 150%;">Here is a video showing exactly how it happens

<span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 150%;">Questions 2
<span style="background-color: #bde7e7; font-family: 'Arial Black',Gadget,sans-serif; font-size: 150%;">4. What was the super-continent called? <span style="background-color: #bde7e7; font-family: 'Arial Black',Gadget,sans-serif; font-size: 150%;">5. Describe what you think the world would have been like 300 million years ago (hint..use your imagination...don't just tell me it had one continent!) <span style="background-color: #bde7e7; font-family: 'Arial Black',Gadget,sans-serif; font-size: 150%;">6. Write down the definitions of theory and tectonics IN YOUR OWN WORDS.