Movement of the earth’s crust

Vocabulary Crust Rift Mantle Sea-floor spreading Core Earthquake Lithosphere Focus Asthenosphere Epicenter Plate tectonics P wave Divergent boundary S wave Transform fault boundary Surface wave Richter scale Mid-ocean ridge volcano

Lesson 1 What are Earth’s Layers? OBJECTIVES You will find out… about the Earth’s structure about Earth’s plates and where they are located some of the ways that Earth’s surface changes.

Earth’s Layers Earth’s basic structure is that of a layered ball. What are the three main layers of Earth? Crust Mantle Core What is Earth’s innermost layer and what is it made up of? The Earth’s innermost layer is the inner core. The inner core is made mainly of iron.

What is the outer core made of? The outer core is made up of mainly iron and nickel. What is the layer above the outer core? The mantle is the layer above the outer core. What is the layer that we live on? We live on the crust. How is it different form the other layers? The curst is the thinnest layer, and it is composed mostly of granite (within continental crust) and basalt (within the oceanic crust).

Use Process Skills Compare the lithosphere to the asthenosphere. In what layer(s) of the Earth is the lithosphere found? The lithosphere includes all of the crust and part of the upper mantle. In what layer(s) of the Earth is the asthenosphere? The asthenosphere includes part of the upper mantle.

Label the layers of Earth

Earth’s Plates Earth’s lithosphere is divided into seven major plates that float on the asthenosphere. What is plate tectonics? The theory scientists use to explain plate movements. Where is Earth’s oceans and continents located? On the plates of the lithosphere.

How can the huge, rigid plates float on the asthenosphere? The asthenosphere has a property called plasticity, which means that it can flow. As the asthenosphere flows, the plates of the lithosphere move with it. Why don’t we feel the ground moving as the plates of the lithosphere move around? Their motion is so slow-just a few centimeters a year-that we don’t feel.

Visual Learning Examine the map of the plates on pages D8-D9. Which plate do we live on? Nearly all of mainland United States is on the North American plate. Which continent seems to fit together with Africa? Possibly South America. Based on their fit, what can you hypothesize about these two continents? South America and Africa used to be part of one larger continent, but now they are moving away from each other.

Changes to Earth’s Surface What changes Earth’s surface? Earth’s surface changes through a process described by the theory of plate tectonics through erosion and deposition caused by wind, water, and glaciers through meteorites that fall to Earth.

Which changes build up Earth’s Surface? The movement of plates The process of deposition by wind, water, and glaciers Which changes wear down Earth’s surface? Erosion caused by wind, water, glaciers, or a hit by a meteorite.

Lesson 2 How Do Earth’s Plates Move? OBJECTIVES You will find out… about divergent, convergent, and transform fault boundaries how continents move and change

The Movement of Earth’s Plates As lithospheric plates move, they interact in one of several ways. How does the movement of plates affect Earth’s surface? Plate movements are responsible for most of the world’s volcanoes, earthquakes, high mountain ranges, and deep-ocean trenches.

What happens along a divergent boundary? Plates move away from each other. Magma oozes up into the opening, forming new crust. What happens along a convergent boundary? Plates collide. The edge of one plate moves down into the asthenosphere and is melted by the high temperatures there. What happens along a transform fault boundary? Plates grind past each other without forming new crust or melting old crust.

Divergent Boundaries What happens along a divergent boundary? Two of Earth’s plates move apart. Hot magma oozes into the gaps, forming new crusts. What do you infer about the magnitude of pressure in Earth’s crust under Iceland? The pressures under Iceland are great since magma erupts as a volcano only where the pressure is great enough.

Convergent Boundaries Three kinds of collisions are possible along a convergent boundary. What happens along a convergent boundary? Two of Earth’s plates collide. One plate may move down under the other plate, or the plates may fold and crumple, forming mountains. The collisions may produce volcanoes and earthquakes.

What happens when two oceanic plates collide? The plates crumple and fold, forming mountain ranges. What happens when an oceanic plate collides with a continental plate? The oceanic plate is forced downward because its crust is denser than continental crust. Mountains and volcanoes form along the convergent boundary.

Transform Fault Boundaries What happens along a transform fault boundary? Two of Earth’s plates grind past each other. What occurs often at transform fault boundaries? Earthquakes may occur often.

Use Process Skills Along what kind of boundary is crust produced? A divergent boundary. Along what boundaries is crust destroyed? Convergent boundaries. Along what boundaries is crust neither formed or destroyed? Transform fault boundaries.

Visual Learning Use the maps on pages D18-D19 to answer the questions. What theory do these maps help illustrate? The theory of plate tectonics. What can you infer about the location of continents from the maps? Continents have not always been in their current position. They have changed position over time.

Earth’s Surface Changes Over Time How do Earth’s plates affect the positions of the continents? As the plates move around Earth's surface, they carry the continents, changing their positions over time.

Lesson 3 What Causes Earthquakes & Volcanoes? OBJECTIVES You will find out… How plate movements cause earthquakes and volcanoes. About the different types of volcanoes.

Plate Movements Cause Earthquakes Earth’s crust is constantly moving and changing. Some of these movements cause earthquakes. How does the movement of plates cause earthquakes? As the plates move, the rocks along their edges become locked together. They bend and stretch until they reach their breaking point. Then they snap, releasing energy that is felt as an earthquake.

Where do most changes in Earth’s crust take place? Along plate boundaries Why don’t we notice most of these changes? They are so slow that they are nearly undetectable. Why do we notice major earthquakes? A major earthquake releases enough energy to cause major damage to buildings and roads. Where do most earthquakes occur? At or near the edges of moving plates, along faults.

Earthquake Waves How is the motion of a P wave different from the motion of an S wave? P waves are “push-pull” waves and travel faster S waves cause vibrations at right angles to the direction of wave travel. Of the three types of seismic waves, which travels the fastest? Primary (P) waves Which travel the slowest? Surface (S) waves

Which wave causes the most damage? Explain. Surface waves; because of their rolling and swaying motion.

Earthquake Safety Scientists measure earthquakes in different ways. What is the difference between the Richter scale and the Mercalli intensity scale? Richter scale measures earthquake energy. The Mercalli scale measures damage done by an earthquake. Volcanic eruptions that caused disasters long ago are always measured on the Mercalli scale. Explain why. The Richter scale measures energy, so it cannot be used for measuring eruptions that occurred in the past. The Mercalli scale measures damage, the evidence of which remains.

How Volcanoes Form Most volcanoes form along plate boundaries. How does a volcano form? A volcano forms when molten rock erupts or flows as lava from an opening in Earth’s surface and builds up a volcanic cone. What is a volcano? A volcano is a mountain that forms when molten rock erupts or flows as lava from an opening in Earth’s surface. Along what types of plate boundaries do most volcanoes occur? Either at rifts where two plates diverge At convergent boundaries, where two plates collide.

Visual Learning Use the graphic sources and captions on pages D26-D27 to answer the following questions. What do you observe about how the shield, cinder cone, and composite volcano are shaped? The shield volcano has a broad, slightly domed shape. The cinder cone and composite volcanoes both have a cone shape.

How are the size and shape of a volcano determined? The size and shape of a volcano are determined by the type of magma that erupts. Runny lava spreads far from the vent, building up a gentle slope, as in a shield volcano. Thicker lava erupts more violently and produces more ashes and cinders that pile up to form a steep cone-shape, as in the cinder cone and composite volcanoes.

Use Process Skills Compare the three types of volcanoes. What are the three kinds of volcanoes? Shield volcano Cinder-cone volcano Composite volcano What can be true for both a cinder cone volcano and a composite volcano? They are both cone shaped and erupt violently. What can be true for both a shield volcano and a composite volcano? they erupt gently and may erupt for 1,000,000 years.

Use Process Skills What is true only for a shield volcano? It is broad, slightly domed shape. They are the world’s largest volcanoes. What is true only for composite volcano? It switches between quiet and violent eruptions What is true only for a cinder cone volcano? It erupts for a short period of time and gets no taller than 300m

Hot Spot Volcanoes What is a hot spot? A hot spot is a narrow column of hot magma that breaks through the lithosphere in the middle of a plate to build a volcano. What is the first step in the formation of a chain of volcanic islands? Within a plate, a volcano forms above a column of hot magma.

How does the motion of the plate produce a chain of islands? As the plate moves, the hot spot below remains stationary. As the plate moves, the first volcano formed dies out and a second volcano forms over the hot spot. This process continues as the plate continues to move over the hot spot, eventually forming a chain of volcanic islands.