Linda F. Malanson
Earth’s plates have been moving around and pulling apart and bumping into each other for a long time. It’ s no wonder the world has gone through a lot of changes.
Take our continents, for instance . . . You may have looked at a globe or map of the world and thought that the continents look like puzzle pieces. If you moved them around, some of them would fit together. Look at South America and Africa—if you pushed them towards each other, they’d match up perfectly side by side! Maybe they were connected once, and then floated apart . . .
Floated apart? The continents? Millions of tons of rock? Can you believe it? Until recently that was pretty much how most scientists reacted when anyone suggested that maybe the continents had been connected long ago and then somehow moved apart.
A German scientist, Alfred Wegener, was the first to study the idea and say that it might be true. He came up with some pretty convincing evidence, too. He discover that the same types of rock and fossils of the same kinds of creatures could be found in places where the continental “puzzle pieces” fit, even though those places were separated by hundreds of miles of oceans.
But it wasn’t until 50 years after Alfred Wegener’s death that geologists realized he was right . . . The continents and ocean floors really do “float” on moving rock plates and have been for millions of years.
They’re floating right now. If a child who is now ten years old—North America and Europe are about one foot farther apart today than they were on the day this child was born. In some places the continents are moving about 2.54 cm (1 inch) a year. In other places, they’re drifting as much as 10 cm (4 inches) a year. Over time continents drifting a few inches a year can make a BIG difference.
About 250 million years ago all the continents on Earth were connected in a single land mass near the equator. Alfred Wegener called it Pangaea which means “all earth”. Around 200 million years ago, Pangaea split into two super-continents that gradually drifted apart. Laurasia, in the north, included the land that would become North America, Europe and Asia. Gondwana, in the south, included South America, Africa, India, Antarctica and Australia.
Over the next 100 million years the land that was to become India drifted northward and eventually crashed into Asia, creating a huge pileup of rock we call the Himalayas. (See Experiment 7B) A split opened between South America and Africa and also between North America and what would be Europe and Asia. The narrow strip of seawater in the middle was a baby ocean. We now call it the Atlantic.
With the help of computers, geologists are using their knowledge of how and where plates move to figure out what our world might look like in the future. Some predict that the Mediterranean Sea will disappear, that the Red Sea will become a new ocean, and that Australia will float to the equator. These changes are expected to take about 75 million years to happen!
(figure available in print form)
(figure available in print form)
(figure available in print form)
(figure available in print form)
EXPERIMENT: PANGAEA, LAURASIA AND GONDWANA
(figure available in print form)
This experiment show how heat moves water and also how a material floating on a moving liquid moves with it. Imagine that the water is the slowly moving bottom layer of the Earth’s crust.
MATERIALS NEEDED:
1. 1.9 liter (2 quarts) cooking pot, full of water
2. stove
3. some dried herbs, such as rosemary, basil or oregano—or some dry sawdust
4. notebook
5. pencil
DIRECTIONS:
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1. AN ADULT HAS TO HELP CHILDREN WITH THIS EXPERIMENT!!! This is necessary because of the stove and boiling water. Place the pot half on and half off one of the burners. (You are trying to make one part of the pot hotter than the other.)
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2. Turn on the stove burner to high. As the water begins to boil (you’ll see tiny bubbles forming on the bottom of the pot), sprinkle a thin layer of dried herbs or sawdust on top of the water. Watch what happens. Think of the dry particles as the earth’s crust plates riding on the liquid mantle of the earth.
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3. Notice where the herbs or sawdust go. Where do the particles gather? Do they gather over the hotter or the cooler part of the pot? Why? What does the movement of the herbs or sawdust tell you about the movement of the water? The dry particles gather where the cooler current sinks and moves away from the spot where the hotter water rises. Why does this happen? Make notes of your observations.
EXPERIMENTS: MOUNTAIN BUILDING
(figure available in print form)
These three experiments demonstrate the process by which many mountain ranges were created. Of course, it takes hundreds and hundreds of years for a mountain range to develop, but these simple experiments will let you imagine how great slabs of the earth’s crust moving toward each other could push up mountains.
MATERIALS NEEDED:
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1. 2 large chunks of clay (either ceramic clay or plasticine), each twice as big as your fist
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2. rolling pin
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3. dull table knife
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4. 2 pieces of aluminum foil, each about 13 cm (5 inches) long
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5. fat dowel or a piece of an old broomstick
DIRECTIONS:
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1. Work the lumps of clay with your hands until they are soft and easy to bend and shape.
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2. Roll each chunk out until it is about 20 cm (8 inches long), 10 cm (4 inches) wide and 5 cm (2 inches) high. Trim the chunks with the knife so that they look like bricks.
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3. Place each clay brick onto the edge of a piece of aluminum foil. Each brick will represent a land mass.
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4. Place the two land masses—each riding on its aluminum foil plate—about 30 cm (1 2 inches) apart on a smooth table or countertop.
Experiment #1—Hold each land mass at its far end and slam them together as hard as you can. Try this several times. Describe what happens. Describe how the clay after the collision is like the edge of a continent that has had a collision with another continent.
Experiment #2—Separate the clay and form it into bricks again. Place the long side of each brick along an edge of its aluminum foil. Push the two bricks so that they brush against each other as they travel past each other. Describe what happens. How is the edge of the clay like an edge of a continent that has had another land mass slide alongside it? Often one land mass is heavier than the other, and it sinks under the lighter land mass as the two collide.
Experiment #3—Here you will use a dowl to lift one clay brick over the other. First make the clay into two bricks again. Sit one of them on a piece of aluminum foil. Place the other brick facing the first brick, but with one of its short ends tilted up so that it rests on the dowl. Slide the two bricks toward each other and jam them together. What happens as they hit each other? How is this collision different from the first or second one that you tried. What kind of land forms would be the result of a collision like that?