What Causes Plates to Move? By Patti Hutchison

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1 Name: Date: Hour: What Causes Plates to Move? By Patti Hutchison 1 They say a watched pot never boils. But do you know what happens when a pot of water does boil? The water is hotter near the bottom where the heat source is located. The cooler water on top sinks to the bottom. The hotter water on the bottom is pushed to the top. This is a kind of convection current. 2 Scientists think convection currents are what cause earth's plates to move. A convection current is caused by differences in temperature. Mantle material close to earth's core is very hot. Mantle material near the lithosphere is cooler. 3 The cooler, denser material sinks toward the core. The hot material near the core expands and becomes less dense. It rises and takes the place of the cooler material. The sinking material becomes hotter and rises. This is a continuous circular motion. 4 Earth's convection currents can be thousands of kilometers across. But they move very slowly. They flow at rates of a few centimeters per year. Scientists believe this movement of mantle material carries the plates of the lithosphere with it. It causes the plates to move. 5 The rising material in this convection current spreads out. It pushes the plates upward and outward. These are divergent boundaries. The material moving downward in the current pulls the plates down with it. These are convergent boundaries. 6 The plates of the lithosphere are made of two different types of crust. Most contain both oceanic and continental crust. Only the Pacific plate contains just oceanic crust. As the plates move, these different types of crust cause different events. 7 Oceanic crust is denser than continental crust. As an oceanic plate bumps into a continental plate, the oceanic plate moves under the continental plate. The oceanic plate is subducted. It is forced down into the trench. The continental plate is folded upward. 8 Two continental plates have the same density. When they collide, neither plate is forced downward. The edges of these plates fold upward. Mountains are formed. 9 When two oceanic plates run into each other, one is forced under the other. This forms a deep trench. The crust of the subducted plate melts. The magma flows upward. Volcanoes are formed. 10 Plates move in different directions and at different speeds. These differences cause other events to occur. Scientists believe that they sometimes run together and form one large plate. Other plates break apart. Still others might be subducted into a trench and disappear. 11 What does all this plate movement mean for our earth? Scientists believe that more than 500 million years ago, the land masses were many different small fragments. Later they moved together to form one large mass. This was the continent Wagener called Panagea. It was surrounded by one large ocean. 12 Scientists believe this large mass then broke into two large continents. Over time they broke apart into the continents we know today. Many scientists think that the continents are moving at a rate of one to five centimeters per year. 13 In about fifty million years, the Atlantic and Indian Oceans will become larger. The Pacific will shrink. Africa and Australia will join Asia once again. If this happens, the earth will look very different than it does today. Copyright 2008 edhelper What Causes Plates to Move? 1. What causes a convection current? 2. What are Earth's convection currents? 3. What occurs when an oceanic plate meets a continental plate? 4. What is formed when two continental plates collide? 5. What happens when there is a collision of two oceanic plates? 6. What do scientists think will happen to Africa, Asia, and Australia if continental drift continues?

2 Name Explain what happens in a convection current. What Causes Plates to Move? Date Explain how mountains and volcanoes are formed.

3 Name: Date: Hour: The Layered Earth By Patti Hutchison 1 Have you eaten a boiled egg? If you have, you know that it has are three layers. The earth also has three layers, much like an egg. 2 An egg has a thin outer shell. Earth does also. This is called the crust. If you run your finger over the shell, you will feel small bumps. The shell can be thicker in some parts than in others. The earth's crust is like this, too. 3 The crust of the earth is very thin and rigid compared to the other layers. There are two types of crust, oceanic and continental. Beneath the ocean, the crust is only about five kilometers thick. The average thickness of crust below the continents is about thirty kilometers. But under mountain ranges it can be as deep as 100 kilometers. 4 Oceanic crust contains mostly oxygen and silicon. Continental crust is made up of two layers of rocks. The top layer is made of granite. The bottom layer is basalt. Elements in the earth's crust include aluminum, iron, sodium, and calcium. Like an egg shell, earth's crust can easily be broken. 5 The crust is the upper part of the lithosphere. This is the solid, top part of the earth. It is broken up into at least seven sections called lithospheric plates. 6 About 50 kilometers below earth's surface lies the mantle. It extends to a depth of 2900 kilometers. The mantle makes up 80 percent of earth's volume and contains about 68 percent of its mass. The mantle can be compared to the white of the egg 7 The mantle is denser than the crust. It is divided into two layers, the upper mantle and the lower mantle. The upper mantle is cooler and denser than the lower mantle. It is also part of the lithosphere. 8 Below the lithosphere is a layer called the asthenosphere. The temperature of this layer ranges between 700 and 1300 degrees Celsius. Here the rock is somewhat molten. It is not rigid; it moves like a thick liquid. Scientists believe that the continental plates float on this layer. 9 The lower mantle begins at a depth of about 1000 km. The temperature varies between 1800 and 2800 degrees Celsius. Pressure also increases with depth. The mantle is made mostly of iron, magnesium, oxygen, and silicon. 10 Below the mantle lies the core. It can be compared to the yolk of the egg. This is the middle of the earth. The core is divided into two parts. The outer core begins at a depth of about 2900 kilometers. It is mostly liquid iron. It has an average temperature of 3200 degrees Celsius. As the earth rotates, the liquid outer core moves. Scientists think this is what causes the earth's magnetic field. 11 About 5100 kilometers below the earth surface is the solid inner core. It has a radius of about 1300 kilometers. It is made of iron and nickel. The temperature is more than 5000 degrees Celsius. At this temperature, iron and nickel usually melt. However, the intense pressure at this pushes the particles together tightly. They remain solid and very dense. 12 Even though no human has gone there, we know a lot about the interior of the earth. If you could journey to the center of the earth, you would go through various layers of solid and molten rock. You would eventually arrive at the solid iron core. Copyright 2008 edhelpe _ 1. The thin outer shell of the earth is called the 2. Name the two kinds of crust. 3. The white of a hard boiled egg is most like which part of the earth? 4. What two layers of the earth make up the lithosphere? 5. Describe the outer core 6. Describe the temperature of the inner core? Why is it this hot?

4 Name The Layered Earth Explain how the layers of the earth can be compared to a hard-boiled egg. Date

5 Name: Date: Hour: How Did the Continents Form? By Patti Hutchison 1 You know that there are seven continents on earth today. But did you know that in the past, the earth looked very different? Sometimes there were more continents. Sometimes there were fewer continents. 2 How did the continents form? The answer is plate tectonics. During the Proterozoic Eon there were hundreds of small pieces of crust floating on the mantle. These first land masses were small continents and island arcs. They collided with each other because of plate tectonics. 3 The pieces of crust hit so hard, they jammed together. At the boundaries, much energy was released. The land fused together. 4 By 2.5 billion years ago, about one-fourth of the earth's crust was formed. These ancient land masses were known as shields. They moved all the time. Larger bodies collided with smaller ones. Mountains were formed at the edges. Lava flowed and welded these pieces together. 5 The first true continent appeared about three billion years ago. It was called Ur. It contained parts of what are now Africa, India, Australia, and Antarctica. 6 Another continent called Artica surfaced about 2.5 billion years ago. It contained what is now North America and part of Asia. 7 Half a billion years later, Atlantica and Baltica were formed. These contained parts of present-day South America, Africa, and Europe. 8 Soon, Baltica and Artica collided. Mountains were formed on both continents. By this time, 80% of the earth's continental crust had been formed. 9 These four continents floated around on the mantle for many years. About 1.5 billion years ago, Artica and Baltica bumped into what is now eastern Antarctica. This formed the continent of Nena. 10 A billion years ago, the continents of Nena, Atlantica, and Ur came together. The supercontinent of Rodinia was born. 11 Three million years later, Rodinia broke up. It separated into three continents once more. Later they came back together to form a new continent. It was called Pangaea. 12 Pangaea was the last supercontinent. It later broke up into the seven continents we know today. Copyright 2008 edhelper How Did the Continents Form? 1. At different times during earth's history there were sometimes less than seven continents. Explain why this statement is true or false. 2. What process formed the continents? 3. What are Ancient land masses were known as? 4. Describe the first true continent: 5. What three continents made up the supercontinent of Rodinia? 6. What was the last supercontinent called? How has the earth changed since then?

6 How Did the Continents Form? Explain in your own words how plate tectonics caused the continents to grow.

7 Name: Date: Hour: Plate Boundaries - Earth's Bumper Cars By Patti Hutchison 1 Have you ever ridden the bumper cars at the amusement park? You drive around on a slippery floor in a car with a huge rubber bumper around it. You move forward and backward, bumping into anyone in your way. The earth's crust is a lot like those bumper cars. 2 The earth's crust is made up of several large plates and some smaller ones. They all float along on the asthenosphere. This is a layer of partly molten rock. It lies under the upper mantle. As these plates move, they bump into one another. Sometimes they move away from each other. The places where they meet are called plate boundaries. 3 There are several types of plate boundaries. Most are found on the ocean floor. The first type is a divergent boundary. This is where two plates move away from each other. A mid-ocean ridge is an example of this type of boundary 4 When the plates move apart, magma flows up between them. It cools and forms new crust. This is why divergent boundaries are also called constructive boundaries. 5 Another type of boundary is called a convergent boundary. This is where plates come together. One plate is pushed under another. These boundaries are also called destructive boundaries. Plate material is destroyed by subduction here. It is melted into the mantle. A deep-sea trench is an example of a convergent boundary. 6 As plates collide along convergent boundaries, there is much friction and pressure. Earthquakes often occur. They can be severe. As the plate material is subducted, some of it flows upward and produces volcanoes. 7 The Ring of Fire lies along the Pacific plate. This is the largest plate on the earth's surface. The Ring of Fire is a line of volcanoes that are found along major trenches in that area. Many of these volcanoes are active 8 Other boundaries are called transform faults. A fault is a deep crack in the earth's surface. At these boundaries, the plates slide past each other. Crust is neither produced nor destroyed at these boundaries. Most of these boundaries are found on the ocean floor. 9 However, there is a famous transform boundary found on land. This is the San Andreas fault zone in California. This fault zone is about 1,300 kilometers long and more than ten kilometers wide in some places. It runs through about two-thirds of the state. Here the Pacific Plate grinds past the North American Plate. They move about five centimeters per year. There are often earthquakes along this fault. 10 As we stand on the earth's crust, we are actually riding on a giant raft. The earth's surface is made up of huge plates that float on molten material. Most of the time, we can't feel the motion because it happens very slowly. If these plates collide, however, we feel and see the effects. Earthquakes and volcanic eruptions are the result of these rafts bumping into each other. These events change the surface of the earth. Copyright 2008 edhelper Plate Boundaries - Earth's Bumper Cars 1. A boundary where plates move away from each other is called. 2. Why is a divergent boundary also called a constructive boundary? 3. An example of a convergent boundary is a. 4. A deep crack in the earth's surface is called a. 5. How do the plates move at a transform boundary? 6. Earthquakes and volcanoes occur at plate boundaries. Explain why this statement is true or false.

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