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Science 10 Plate Tectonics UNIT 1

PLATE TECTONICS

PART A THE DYNAMIC EARTH

Table of Contents:Description Complete

?Structure of the EarthDirect and Indirect ObservationsContinental DriftThe Theory of Plate TectonicsSea-Floor Spreading

The Learning Centres page 1 of 42


WHAT IS THE STRUCTURE OF THE EARTH

crust: thin, solid outer layer of the Earth

mantle (MAN-tul): thick layer of rock below the crust

lithosphere (Lith-us-fear): the crust and the solid part of the upper mantle

asthenosphere (az-THEEN-us-fear): semi-liquid upper part of the mantle

outer core: outer layer of the core, made of liquid iron and nickel

inner core: inner layer of the core, made of very dense solid iron

diameter: the distance across a circle or sphere through its center.)

LAYERS OF THE EARTHWhen you were a child, did you ever plan to dig a hole through the earth to the other side? What did you think the inside of the earth is like?

The inside of the earth can be compared to a hard-boiled egg. If you cut a hard-boiled egg with the shell on, you can see that the egg has three different layers. They are the shell, the white and the yolk.The earth also has three main layers. These layers are the crust, the mantle, and the core.

THE CRUSTThe crust is the solid, outer layer of the earth.

The top of the crust is made up of loose rocks and soil. Under the rocks and soil, the crust is rigid, solid rock. We live on the crust.

There are two types of crust. Ocean or oceanic crust is covered by our planet’s oceans. Continental crust is the land on which we live. On average, continental crust is less dense than oceanic crust.

The crust is thick in some places and thin in others. Beneath the oceans, the crust is between 5 km and 10 km thick. Beneath the continents the crust is between 32 km and 70 km thick. Compared to the whole Earth, the crust is very thin. The whole earth is

about 12,700 km in diameter.

THE MANTLEThe layer of the earth beneath the crust is the mantle.

The mantle is about 2800 km thick. The Learning Centres page 2 of 42

Science 10 Plate Tectonics UNIT 1 More than two-thirds of the mass of the earth is in the mantle.

The mantle has two main parts: the Upper Mantle and the Lower Mantle.

The outer part of the upper mantle is solid rock. The inner part of the upper mantle is semi-solid, and is called the

ASTHENOSPHERE. The lower mantle is dense liquid.

The crust and the solid outer part of the upper mantle are collectively called the LITHOSPHERE.

The lithosphere is a solid layer. It is cold and brittle and can fracture during an earthquake.

The lithosphere is divided into pieces called tectonic plates. Below the solid lithosphere is the semi-solid ASTHENOSPHERE.

This part of the upper mantle is hot, semi-solid and can bend like plastic. The tectonic plates of the lithosphere float on the asthenosphere, much like broken ice fragments float on the surface of water.

Because the asthenosphere is too hot to fracture, earthquakes cannot occur in the asthenosphere . The asthenosphere does, however, bend under pressure.

As you can see in this diagram, the lithosphere is made up of the crust and outer part of the upper mantle. Below the lithosphere is the asthenosphere. The lithosphere (which is broken into tectonic plates) floats on the asthenosphere.

THE COREThe two innermost layers of the Earth make up the CORE.

The core is about 3500 km thick. The core has two parts.

The outer core is a liquid layer. It contains melted iron and nickel. It is about 2200 km thick.


Science 10 Plate Tectonics UNIT 1 The inner core is a solid layer. It contains solid iron and nickel. It is

about 1300 km thick. The core is the densest part of the Earth.

The layers of the Earth.

WHAT IS THE STRUCTURE OF THE EARTH? – questions

Complete each statement using a word or words from the list below. Write your answers in the spaces provided. Some words may be used more than once. Some words may not be used at all. 10 marks

asthenosphere mantle outer core lowerinner core crust lithosphere continentaloceanic oceans upper continents

1. Starting with the top layer, the main layers of the Earth are the ___________, the _____________, the __________________, and the ________________.

2. The top of the ______________________ is made up of loose rocks and soil.


Science 10 Plate Tectonics UNIT 13. The thickest crust is found beneath the ______________________.

4. More than two-thirds of the Earth's mass is in the _____________.

5. The _________________ contains the crust and the solid outer part of the upper mantle.

6. The semi-solid part of the upper mantle is called the ________________.

7. The layer that has melted iron and nickel is the _____________________.

8. The ____________________ is made up of solid iron and nickel.

9. The layer of the Earth between the core and crust is the ________________.

10.The densest type of crust is the __________ crust .

Match the thickness with the correct earth layer by writing the correct letter on the line in front of the thickness of each layer. 4 marks

____ 1300 km thick a. the outer core

____ 2800 km thick b. the crust

____ 5 - 70 km thick c. the mantle

____ 2200 km thick d. the inner core

WHAT ARE DIRECT AND INDIRECT OBSERVATIONS?

Until about 100 years ago, all that was known about the structure of the Earth was that it is spherical and has a diameter of about 12 700 km at the equator. Scientists now know a lot more about the structure of our Earth. They have made their discoveries through both direct and indirect observations.

DIRECT OBSERVATIONSDirect observations are those that you can see directly. They are the most accurate type of observation. Examples of direct observations include:

Lava Samples: Volcanoes provide us with information about the Earth’s interior without actually going there! Scientists can sample the lava to determine all sorts of data. The Learning Centres page 5 of 42

Science 10 Plate Tectonics UNIT 1Core Samples: A special drill is used to bring up tubular layers of rock, called core samples. Scientists can use these to “see” the layers of rock deep below the Earth’s surface.

Sampling Lava Core Samples

Remote Sensing: Another type of direct observation that allows scientists to learn about the Earth’s structure is remote sensing. Remote sensing simply means to get information from a distance. Remote sensing techniques include satellite and aerial photos, the use of GPS (Global Positioning System) receivers, and infrared and radar images.

A satellite image of the Lower Mainlandand Southern Vancouver Island

INDIRECT OBSERVATIONSNot all areas of the Earth can be observed directly. In many cases, scientists use observations made at the surface of the Earth to make suggestions about its inner structures and the processes occurring underground.

Movement inside the Earth causes shock waves called seismic waves. Earthquakes create seismic waves that cause destruction, but seismic waves also tell scientists about the inner structure of the Earth. You will learn more about the different types of seismic waves later in this unit.

EVIDENCE OF A DYNAMIC EARTH

Today, we know that the surface of the Earth is continually moving. New parts of the lithosphere are formed and older sections are recycled. Most scientists think that the lithosphere (the crust of the Earth and solid part of the upper mantle) is broken into pieces called tectonic or crustal plates.


Science 10 Plate Tectonics UNIT 1Below the tectonic plates is the asthenosphere, which is made up of hot rock that flows like thick liquid. The tectonic plates float on the asthenosphere like broken ice fragments float on a lake.

Plate tectonics is the theory that explains this plate movement and its consequences. But this theory took a long time to develop and much evidence was gathered along the way before this theory was accepted. The first step in this process was the theory of Continental Drift. You will learn about this theory next.

WHAT ARE DIRECT AND INDIRECT OBSERVATIONS? - questions

1. Give three specific different direct observation techniques that scientists use to

learn about the structure of the Earth.

__________________________________________

__________________________________________

__________________________________________

2. What do scientists study to learn about the inner structure of the Earth?

__________________________________________



WHAT IS THE THEORY OF CONTINENTAL DRIFT?

Most scientists think that millions of years ago there was one giant continent. A continent is a giant landmass. This giant continent was surrounded by one giant ocean. About 180 million years ago, the continent began to break apart. The pieces of the continent slowly drifted apart. They became today's seven continents.

A German scientist named ALFRED WEGENER was the first to propose the idea that our present continents were once part of a giant landmass that split apart. Wegener called the giant landmass PANGAEA (pan-JEE-uh). He called his idea CONTINENTAL DRIFT.

EVIDENCE TO SUPPORT CONTINENTAL DRIFT

Fit of the Continents: In the early 1900's, Wegener noticed that the continents seemed to fit together. If you look at the coastlines of South America and Africa on a map, you will notice that the coastlines The Learning Centres page 8 of 42

All continents were once joined together in a supercontinent called Pangaea.

Science 10 Plate Tectonics UNIT 1seem to fit together like pieces of a jigsaw puzzle. Other places can also be found that might once have fitted together. The fit of the continents is one clue that supports continental drift.

Matching of Mountain Chains: The mountain ranges on different continents seem to match. The Appalachian mountain range along the eastern United States and Canada is similar to one in Greenland and northern Europe. When these landmasses are placed in their pre-drift locations, as the supercontinent Pangaea, the mountains fit together as one continuous chain.

Age and Kind of Rocks: The age and kind of rocks along the edge of one continent match rocks along the edge of other continents. They match at the same locations as the continents would fit together in a model of Pangaea.

Fossil Evidence: Fossils of the same ancient plants and animals are found today on widely separated continents. For example, Wegener discovered that Mesosaurus fossils were found in Africa and in South America. Mesosaurus was a reptile that lived in fresh water. How could it swim across the salty Atlantic Ocean? Wegener concluded that the animal must have lived on one landmass. When the landmass broke apart, some of the animals were trapped on each part.

Paleoglaciation: Evidence suggests that vast ice sheets existed in South America, Africa, India, Australia, and Antarctica about 250 million years ago. However, many of these areas are tropical today. The current position of the continents would lead one to believe that glaciers must have existed in equatorial regions at the same time as tropical climates existed in equatorial regions. This, of course, does not make sense. Today, scientists realize that the areas containing these ancient glaciated landscapes were joined together into the single supercontinent of Pangaea that was located far south of their present positions. This paleoglaciation evidence is further evidence of continental drift. “Paleo” means ancient. The Learning Centres page 9 of 42

Fossils of different animals and plants are found today on widely separated continents, in the same locations where the continents would fit together in a model of Pangaea.


Crustal Movement at Mid-Ocean Ridges: There is evidence that the crust is moving apart at ocean floor locations called mid-ocean ridges. If the ocean crust is moving, then the continents must be moving as well. The next section will explain this concept in more detail.

CHALLENGES TO CONTINENTAL DRIFT THEORYWegner’s theory faced a lot of opposition in the early 1900s. Unfortunately, he could not provide strong enough evidence for how the continents moved over the surface of the Earth. While many science groups were opposed to these new ideas, around the time of World War II, evidence was gathered that allowed his theory to be accepted, advanced and refined into a newer theory. In the next section, you will learn about this newer theory called the Theory of Plate Tectonics.


Current position of the continents, showing areas of ancient glaciers.

Position of glaciers prior to the continents drifting apart.


WHAT IS THE THEORY OF CONTINENTAL DRIFT? questions

Multiple Choice

1. Scientists believe that there was one giant continent

A. hundreds of years agoB. thousands of years agoC. millions of years agoD. billions of years ago

2. The giant continent was called

A. WegenerB. HugeC. PangaeaD. Eurasia

3. This continent began to break apart

A. 180 years agoB. 180 thousand years agoC. 180 million years agoD. 180 billion years ago

4. The scientist who came up with the theory of continental drift was named

A. Alfred WegenerB. Alfred SmithC. John PangaeaD. Harold Eurasia



5. Which of the following are pieces of evidence for continental drift? Circle only the letters of correct answers. Hint: there is more than one to circle!

A. There are landslides on the coasts of the continents

B. The coastlines of some continents seem fit together like a jigsaw puzzle

C. Fossils of the same ancient plants and animals are found today on widely separated continents

D. Similar rocks are found along the coastlines of the continents just where they seem to fit together like a jigsaw puzzle

E. Some mountain ranges on different continents seem to match along the coastlines

F. There are mountains on all of the continents

G. There is evidence of ancient glaciation just where the continents seem to fit together like a jigsaw puzzle

H. The crust is spreading apart at the mid-ocean ridges

I. Scientists can see the continents drifting apart



WHAT IS THE THEORY OF PLATE TECTONICS?

Introduction:During World War II, sound waves were bounced off objects to measure how deep they were. This was very useful in detecting enemy submarines. But it had another benefit, too. Scientists determined that the ocean floor was not flat and featureless, but covered with trenches, crevasses, mountain ridges and volcanoes! After the war when trans-Atlantic telephone cables were being laid, engineers found an undersea mountain range. Oceanographers determined that this range ran the entire length of the ocean, right up the middle. Named the Mid-Atlantic Ridge, scientists found it had a deep, wide canyon running the length in its centre. This deep crack is called a rift valley. Other mid-ocean ridges were also discovered, as well as deep ocean trenches along the edge of some continents.

As scientists gathered more information about Earth, they began to notice that most earthquakes, volcanoes, mountain ranges and ocean trenches are located along certain boundaries.

Volcanoes and earthquakes are found along ocean ridges and trenches.



This discovery led to an expansion of the Continental Drift Theory, to the present theory called the THEORY OF PLATE TECTONICS. The Theory of Plate tectonics states that the lithosphere is divided into 12 large sections called tectonic plates (or just “plates”), and about 20 smaller ones as seen below.

The Earth is divided into tectonic plates. It is at these plate boundaries that the lithosphere is moving and causing earthquakes, volcanoes, ocean trenches, and mountain building.

The THEORY OF PLATE TECTONICS states that the lithosphere is moving at the plate boundaries. This movement is causing earthquakes, volcanoes, ocean trenches, and mountain building.

Each plate moves in a different direction so some plates are moving away from each other, some are moving towards each other, and others are moving past each other in opposite directions.

These plates meet at three types of plate boundaries which are classified (and named) by the relative direction of plate movement. The three types of plate boundaries are: divergent plate boundaries, convergent plate boundaries, and transform plate boundaries.

The three main types of plate boundaries are shown on maps with different map symbols as follows: The Learning Centres page 14 of 42

Science 10 Plate Tectonics UNIT 1 divergent plate boundaries are marked by double parallel lines,

convergent plate boundaries are marked by sawtooth lines, and

transform plate boundaries are marked by single lines.



WHAT IS THE THEORY OF PLATE TECTONICS? - questions

1. The Continental Drift Theory is ________ The Theory of Plate Tectonics. A. newer thanB. older thanC. the same age as

2. Why are earthquakes and volcanic activity common along plate boundaries?

A. no one knows whyB. because plate movement occurs thereC. because plate movement does not occur thereD. None of the above. Earthquakes and volcanoes are not common along plate boundaries.

Completion3. Draw the tectonic map symbol you would see at a

a. Divergent plate boundary

b. Transform fault boundary

c. Convergent plate boundary

WHAT ARE THE THREE PLATE BOUNDARIES?


Science 10 Plate Tectonics UNIT 1As mentioned in the last section, there are three types of plate boundaries. The three types of plate boundaries are:

DIVERGENT plate boundaries, CONVERGENT plate boundaries and TRANSFORM plate boundaries.

In the following pages, you will learn more about how the plates are moving and about the landscape features created by their movement.

.DIVERGENT PLATE BOUNDARIES

The boundary between two plates that are moving apart is called a divergent plate boundary or a spreading center because the plates are diverging, or spreading apart. As the plates spread apart, the gap between them is filled with magma that oozes up from the hot mantle. The molten rock cools slowly to make new

ocean floor. About 5 cm of new crust is created each year at a divergent plate boundary.

At the same time, the rising magma and heat causes the edges of the diverging plates to bulge upward. This creates a mountain called a RIDGE. The mountains running down the center of the oceans are called mid-ocean ridges. Between the ridges, huge blocks of the crust may collapse. This creates a valley called a RIFT VALLEY.

The mid-ocean ridges of the world are connected and form the longest mountain range in the world. Some of its peaks are 3048 m above the ocean floor. In a few places, the peaks rise above the surface of the ocean. These peaks form islands.

Iceland is a mountain peak of the Mid-Atlantic Ridge. The Mid-Atlantic Ridge runs down the middle of the Atlantic Ocean.Divergent plate boundaries can also occur on continents. Perhaps the most famous continental rift valley is the Great Rift Valley found in Africa. It is 4800 km long and runs down the eastern side of the


Ridges and rift valleys form at divergent plate boundaries.

ridge rift valley

Science 10 Plate Tectonics UNIT 1whole continent. It contains some of the deepest lakes and highest mountains on the continent.

CONVERGENT PLATE BOUNDARIESWhile plates are moving apart in one part of the Earth’s crust, other plates are moving toward each other. Another name for “moving toward each other” is “converge”. The boundary between plates that are moving toward each other is called a convergent plate boundary. When two tectonic plates converge, the plate with

the higher density usually subducts (slides under) the other. This collision can create a variety of landscape features.The features that form when plates collide at a convergent plate boundary depend on the types of plates involved. Three types of collision are possible. Collisions can take place between:

- an oceanic and a continental plate, - two oceanic plates or - two continental plates.

Collision Of An Oceanic And A Continental Plate: When an oceanic and a continental plate collide, the oceanic plate

will subduct (slide under) the continental plate. This happens because the oceanic plate is denser than the continental plate.

The subducting crust is drawn into the hot mantle, where it melts... it is recycled to become new mantle.

The region where one plate descends into the asthenosphere is called a SUBDUCTION ZONE.

As the oceanic plate slides beneath the overriding plate, the oceanic plate bends and produces an oceanic trench and a mountain chain (that includes volcanoes) parallel to the trench.



You can see from this diagram that an oceanic trench is formed when one plate subducts under another. The area where the subduction takes place is called a subduction zone. Subduction takes place at convergent plate boundaries. Crust melts as it sinks into the hot mantle.

Collision Of Two Oceanic Plates: If two oceanic plates collide, the denser one will subduct under

the less-dense one. The subducting crust is drawn into the hot mantle, where it

melts ... it is recycled to become new mantle. As in any subduction zone, an oceanic trench is created between the

plates. Mountains and volcanoes are also created parallel to the trench, which may become islands if they are tall enough. The Philippines were created in this way.

Collision Of Two Continental Plates: If two continental plates collide, neither plate can slide beneath the

other because continental crust is light and cannot sink into the mantle. The plates will buckle upwards and fracture instead. This will create mountains.

An example of this is where India collided with Asia, forming the Himalayan Mountains.

One further result of subduction is that some of the Earth’s crust gets recycled as it sinks into the hot mantle. However, some of the Earth’s crust never subducts. As a result, not all of the Earth’s crust is the same age. Let me explain.

Continental crust is less dense than the ocean crust and so it does not subduct. It is forever pushed around the surface of the Earth and consequently contains the oldest rocks on Earth, up to 4 billion years old.

Ocean crust does subduct at convergent plate boundaries. When it subducts, heat and pressure cause it to melt into the mantle (usually at depths of about 700km). It is continually being recycled and so it is much younger than continental crust.


Figure to the left:A trench is formed between the plates at a subduction zone.

Mountains and volcanoes are also formed on the overriding plate (the one on the top) as it pushes over the subducting plate.


TRANSFORM PLATE BOUNDARIESAt a transform plate boundary, plates slide past each other in opposite

directions. Neither plate rides up over the other, nor does either plate subduct (slide under) the other. Crust is neither created nor destroyed at transform fault boundaries. Transform plate boundaries are also called strike-slip faults. Earthquakes often occur when these plates slide. The most famous of this type of boundary is the San Andreas Fault in California. Cracks in the Earth’s surface can often be

seen at transform plate boundaries.

SUMMARY

WHAT ARE THE THREE PLATE BOUNDARIES? - questions

Multiple Choice

1. Divergent boundaries are also called

A. widening boundariesB. converging boundariesC. spreading centersD. oozing boundaries

2. The plates at a divergent boundary are

A. moving apart from each other B. moving towards each otherC. sliding past each otherD. not moving at all


In summary, there are 3 types of plate boundaries: Transform plate boundaries (also called transform faults or

strike-slip faults) are where plates slide past each other Divergent plate boundaries (also called spreading centres)

are where plates are moving apart from each other. Convergent plate boundaries are where plates are moving

toward each other.

Science 10 Plate Tectonics UNIT 13. The plates at a convergent boundary are


4. The plates at a transform fault boundary are


5. Another name for transform fault boundary is

A. sliding boundary B. side-to-side boundaryC. strike-slip faultD. sliding fault

6. New ocean floor crust is being produced at

A. convergent boundariesB. divergent boundariesC. transform fault boundariesD None of the above: no new ocean floor is being produced today.

7. Crust is being destroyed at

A. convergent boundariesB. divergent boundariesC. transform fault boundariesD. None of the above. Crust is not being destroyed today.

8. When an oceanic and a continental plate collide,

A. the continental plate will slide under the oceanic plateB. both plates will buckle upwardC. the oceanic plate will slide under the continental plateD. both plates will move downwards

9. When two oceanic plates collide,

A. the heavier plate will slide under the lighter plateB. the lighter plate will slide under the heavier plateC. both plates will buckle upwardD. both plates will descend into the asthenosphere

10.When two continental plates collide, The Learning Centres page 21 of 42

Science 10 Plate Tectonics UNIT 1A. one continental plate will slide under the otherB. both plates will buckle upwardC. both plates will move downwardsD. None of the above. Two continental plates never collide.

11. The place where one plate slides under another and descends into the asthenosphere is called a

A. subduction zoneB. divergent zoneC. transform fault zoneD. None of the above. One plate does not slide under another plate.

12. Oceanic trenches are created between the plates at

A. convergent boundariesB. divergent boundariesC. transform fault boundariesD. All of the above. E. None of the above. Oceanic trenches are not being created today.

13. Mid-ocean ridges are created between the plates at

A. convergent boundariesB. divergent boundariesC. transform fault boundariesD. All of the above. E. None of the above. Mid-0cean ridges are not being created today.

14.Oceanic trenches form when

A. a heavy plate subducts under a lighter plateB. lighter plate subducts under a heavier plateC. two light plates subduct togetherD. two heavy plates subduct together

15.The collision of a continental and an oceanic plate will result in the formation of (choose all correct answers … there are more than one)

A. a trenchB. a subduction zone.C. MountainsD. Volcanoes

16.The collision of two continental plates will result in the formation of

A. a trenchB. a subduction zoneC. mountains

17.Rift Valleys form at


Science 10 Plate Tectonics UNIT 1A. divergent plate boundariesB. convergent plate boundariesC. transform plate boundariesD. subduction zones



WHAT’S THE EVIDENCE FOR SEA-FLOOR SPREADING?

As mentioned previously, plates are spreading apart at divergent plate boundaries. The plates spread apart because molten rock rises up through the cracks in the rift valley of the mid-ocean ridge. As the magma cools, it forms new crust on both sides of the rift valley. This causes the sea floor to spread apart as the new crust is formed and pushes away the older crust on both sides of the rift valley. This process is sometimes called SEA-FLOOR SPREADING.

Scientists have compiled the following evidence to prove sea-floor spreading.

Paleomagnetism and Geomagnetic Reversals: The Earth is like a giant magnet. It has a magnetic field similar to that produced by a bar magnet. Minerals that contain iron, such as magnetite, have magnetic properties. When lava containing these minerals cools, the iron-rich grains become magnetized in the direction of the existing magnetic field. If the rock is moved, the magnetized mineral grains will retain their original alignment. The iron particles in rocks forming today point north because that is the direction of the current magnetic field. The iron particles in rocks that formed millions of years ago point in the direction of the magnetic pole at the time and place of their formation. They are said to possess PALEOMAGNETISM.

If the Earth’s magnetic field has not changed through its history, the magnetic particles in rocks should point north. However, scientists have discovered rocks with magnetic particles that point south. This suggests that the Earth’s magnetic field has changed through its history. North became south; and south became north. Scientists call this phenomenon GEOMAGNETIC REVERSAL.


A RIFT VALLEY is a deep crack running down the centre of mid-ocean ridges.

Science 10 Plate Tectonics UNIT 1Scientists have used their knowledge of paleomagnetism and geomagnetic reversals to prove the sea floor is spreading at divergent plate boundaries.

Using a special instrument called a magnetometer, they found an interesting pattern as they moved outward from either side of the ridges.First there is a strip of rock with magnetic particles pointing north. Then there is a strip of rock with magnetic particles pointing south . Then north and then south as you move outward from the ridge. These strips run parallel to the mid-ocean ridges. They form a mirror image pattern on the ocean floor at the mid-ocean ridges.

Why?

The plates are spreading apart at the mid-ocean ridges. As they move apart, new ocean crust is constantly being created as magma moves upward and cools on both sides of the mid-ocean ridge. During the periods when the magnetic pole is in the north, the magnetic particles point north. During the periods when the magnetic pole is in the south, the magnetic particles point south. This pattern shows that new crust is being created on either side of the mid-ocean ridges and that the crust is moving.

Deep-Sea Drilling:Further evidence for sea-floor spreading has come from deep-sea drilling. Deep-sea drills have been used to bring up samples of oceanic crust. Scientists have used radioactive dating techniques to determine that these samples of oceanic crust are younger than samples of continental crust. Also, the crust near a mid-ocean ridge is younger than the crust farther away from the mid-ocean ridge. The youngest crust is in the center of the ridge.

WHAT’S THE EVIDENCE FOR SEA-FLOOR SPREADING? - questions

Multiple Choice



1. A rift valley is

A. a shallow crack running down the center of a mid-ocean ridgeB. a very long mountain chainC. a valley found in IcelandD. a deep crack running down the center of a mid-ocean ridge

2. The sea-floor is

A. spreading apart at the mid-ocean ridgesB. moving together at the mid-ocean ridgesC. not moving at allD. spreading apart only near Iceland

3. Where does sea-floor spreading occur?

A. strike-slip faults B. subduction zonesC. mid-ocean ridges D. deep ocean trenches

4. When molten rock containing iron-rich minerals cool, the grains will point in the direction of the Earth's magnetic field. This fact is called

A. sea floor spreadingB. paleoglaciationC. geomagnetic reversalD. paleomagnetism

5. Throughout history, the Earth’s magnetic field has changed from north to south and visa versa. This fact is called

A. sea floor spreadingB. paleoglaciationC. geomagnetic reversalD. paleomagnetism

6. Which of the following diagrams provide evidence for sea-floor spreading?



A. I only

B. I and II only

C. II and III only

D. IV only

7. The crust near the mid-ocean ridges is

A. older than the crust farther out from the mid-ocean ridges.B. the same age as the crust farther out from the mid-ocean ridges.C. younger than the crust farther out from the mid-ocean ridges.



PART BPLATE TECTONICS: CAUSE AND EFFECT

Table of Contents:Description Complete

?Causes of Plate MovementEffects of Plate Tectonics – Landscape FeaturesEffects of Plate Tectonics – Geologic EventsEffects of Plate Tectonics – Seismic Waves

WHAT ARE THE CAUSES OF PLATE MOVEMENT?

Scientists believe that there are three forces that move tectonic plates: convection currents in the mantle, ridge push, and slab pull.



Mantle convection, ridge push, and slab pull combine to move tectonic plates.

Mantle ConvectionConvection is the vertical movement of a gas or a liquid caused by differences in temperature. When hot liquid iron and nickel rises in the mantle, it cools, and then sinks in another place. This up and down movement forms a CONVECTION CURRENT. You have probably seen a convection current in a pot of soup on the stove. Particles in the soup rise and then sink and then rise and then sink again in a circular motion.

When hot mantle rises in one place, cools, and then sinks in another place, this convection current is known as MANTLE CONVECTION. This current in the asthenosphere is one of the forces that move the tectonic plates, and the continents of the lithosphere move with them.

Ridge PushWhere the hot mantle rises up at a divergent boundary, it heats the crust above it until the crust expands, becomes less dense, and floats higher. This action makes a ridge, and the crust is pulled thinner; kind of like pushing up on a slab of modeling clay with your finger. Cracks are formed in this thinner area, and magma comes to the surface through the cracks. As this magma cools in the cracks, it wedges the plates apart. As this new sea floor cools further, its density increases and it sinks down. As it sinks, it pushes the


Science 10 Plate Tectonics UNIT 1plate away from the mid-ocean ridge. This push from the ridge is called RIDGE PUSH.

Slab PullAt a subduction zone, a more dense plate collides with a less dense plate, and the more dense plate subducts under the less dense plate. As the edge of the plate descends into the mantle, gravity and convection currents pull the rest of the plate with it. This is called slab pull.

Source of the HeatThe source of the heat that melts the outer core & mantle and that causes the convection currents is the decay of radioactive minerals deep within the Earth. When radioactive substances decay, they release heat. You will learn more about this process in the radioactivity unit later in this course.

WHAT ARE THE CAUSES OF PLATE MOVEMENT? - questions

Multiple Choice1. A convection current is the movement of a gas or a liquid caused by differences in

A. air pressureB. temperatureC. colorD. opinion

2. The mantle rock close to the core is


Summary of the Causes of Plate Movement: Mantle convection currents help to move the plates along.

The edge of a tectonic plate is moved away from the spreading ocean

ridge by ridge push.

Slab pull at the edge of a subducting plate acts to pull the rest of the

plate down into the mantle.

Science 10 Plate Tectonics UNIT 1A. cool B. coldC. warmD. hot

3. Which of the following does NOT contribute to the motion of tectonic plate?

A. Slab pullB. Ridge pushC. Centrifugal forceD. Mantle convection

4. Convection currents that help move the lithospheric plates occur in the

A. mantle B. crust C. inner coreD. outer core

5. Why does the sea floor bulge up and make a ridge at a spreading centre?

A. Heated crust is more dense, so it floats highest.B. Magma piles up as it rises from the mantleC. Heated crust is less dense, so it floats higher.D. Friction curls up the edges of the crust as it moves.

WHAT ARE THE EFFECTS OF PLATE TECTONICS?- VOLCANOES and EARTHQUAKES

The interaction of tectonic plates also causes geologic events like volcanoes and earthquakes which, in turn, further alter the landscape of the Earth.

VOLCANOESA volcano forms at a crack in the lithosphere where magma (molten rock below the surface) and gases reach the Earth’s surface. Once the magma reaches the surface, whether underwater or on a continent, it is called lava. Magma forms deep underground in the asthenosphere when rocks melt. This happens due to one of three events:

a drop in pressure, perhaps from a crack in the crust a change in composition of the rock, perhaps due to a subduction

zone


Science 10 Plate Tectonics UNIT 1 an increase in temperature, perhaps due to a hot spot or

convection current upflow

Volcanoes form at different locations for different reasons.

Volcanoes form at divergent plate boundaries. When tectonic plates diverge, it relieves pressure on the mantle below and the magma flows upward to the surface, forming a volcano.

Krafla Volcano, Iceland, on the Mid-Atlantic Ridge

Volcanoes also form at convergent plate boundaries. These are the most common type of volcano found around the Earth. At convergent plate boundaries, the crust melts and turns to magma as it is pulled into the hot mantle. The magma moves upwards, following cracks formed in the subduction zone. The magma reaches the surface of the overriding plate about 100 - 300 km from the ocean trench formed from the subduction. This creates a row of volcanoes approximately parallel to where the plates meet.

If the plate boundary is an oceanic – continental convergent boundary, a chain of inland volcanoes called a volcanic belt is created. The Cascade Mountains are such a volcanic belt, stretching from southern British Columbia to northern California. The last to erupt was Mount St. Helen’s in 1980. Mount Baker, easily seen from Surrey, is a dormant volcano that lets off a bit of steam once in a while. Mount Garibaldi is a volcano of this range found near Whistler, B.C.

Mt. Baker is a volcano in this chain whose magma is produced when the Juan de Fuca Plate subducts under the North American Plate.


Mount Baker

http://www.physics.unlv.edu/~jeffery/astro/earth/geology/plate/usgs_006_volcano.html%00%E5%A1%B9%EF%92%81%E1%B4%BB%E4%A1%BF%E2%B2%AF%E5%B6%82%E8%97%84%E6%8C%A7%00%00%EA%AE%A5


Subduction zone volcanoes are also formed parallel to an oceanic – oceanic convergent plate boundary. In this case, the chain of volcanoes created is called a volcanic island arc. An example of this occurrence is the Aleutian Islands which stretch across the North Pacific Ocean between Alaska and Siberia, Russia.

Notice how the volcano forms away from the trench, on the overriding plate.

Volcanoes also occur over hot spots. HOT SPOTS are small regions of very hot mantle that are thought to be created by excess radioactivity near the Earth’s core. This heat creates a very hot column of rising mantle which causes the lithosphere to thin out and crack as it bulges up. Eventually, magma bursts through the weakened lithosphere over the hot spot, forming a volcano. Hot spot volcanoes can form in oceanic crust and continental crust.

The hot spot stays in one place while the lithosphere moves over it. As the tectonic plate continues to move, the location on the plate overtop of the hot spot changes. The original volcano moves away from the hot spot and a new volcano is formed.

Over time, a chain of volcanoes is formed, stretching away from the hot spot in the direction of the plate movement. If the hot spot is beneath the ocean, the volcanoes form a chain of islands. The Hawaiian Islands are an example of a hot spot volcanic island chain.



Volcanic Island Chains can form from hot spots deep within the asthenosphere.

If the hot spot is beneath a continent, a chain of land volcanoes is created like the Anahim Belt located in southwestern B.C.. Yellowstone Park in the continental USA is also located over a hot spot.

EARTHQUAKESAs convection currents, ridge push, and slab pull try to move tectonic plates, friction between the plates resists the movement. When the forces trying to move the plate become stronger than the force of friction resisting the movement, the plates move suddenly and release a massive amount of energy. This sudden, strong movement in the Earth’s crust is called an earthquake. Small movements of the crust you may or may not feel are called tremors. There are more than six million tremors on Earth each year. The actual location inside the Earth where an earthquake starts is called the focus. The place on the surface of the Earth directly above the focus is called the epicenter. Earthquakes can occur anywhere on Earth. However, 95% occur at tectonic boundaries and about 80% of all earthquakes occur in a ring around the Pacific Ocean commonly known as the Pacific Ring of Fire.



The “Pacific Ring of Fire”

Scientists categorize earthquakes according to how far beneath the Earth’s surface the focus occurs. There are three categories:

shallow-focus earthquakes, where the focus is up to 70 km deep and occurs in the crust;

intermediate-focus earthquakes, where the focus is 70-300 km deep and occurs in the subduction zone; and


Science 10 Plate Tectonics UNIT 1 deep-focus earthquakes where the focus is 300-700 km deep and

occurs in the mantle.

Earthquake Categories

Earthquakes occur at all types of plate boundaries.; the plates could be sliding past each other along a transform fault, they could be pulled apart at a divergent boundary, or they could be subducting at a convergent boundary.

This diagram shows possible locations of volcanoes and earthquakes at different types of plate boundaries and hot spots.

A fault is a displacement of the lithosphere – whether vertically, horizontally, or both – created by the movement of tectonic plates.

As the rocks move during an earthquake, they release mechanical energy in the form of vibrations. These vibrations are called seismic waves, or earthquake waves.

WHAT ARE THE EFFECTS OF PLATE TECTONICS – LANDSCAPE FEATURES?- GEOLOGIC EVENTS -

questions


hotspot


Multiple Choice

1. Volcanoes can be found

A. at convergent plate boundariesB. at divergent plate boundariesC. at hot spot locationsD. all of the above

2. Molten rock that reaches the Earth’s surface is called

A. magmaB. lavaC. molten rockD. rock

3. Molten rock that under the Earth’s surface is called

A. magmaB. lavaC. molten rockD. rock

4. Small movements of the crust that you may or may not feel are called

A. shakesB. wavesC. tremorsD. earthquakes

5. Sudden, strong movements of the Earth's crust are called

A. shakesB. wavesC. tremorsD. earthquakes

6. The place inside the Earth where the earthquake starts is called the

A. focusB. epicenterC. seismic wave


Science 10 Plate Tectonics UNIT 1D. starting point

7. The place on the Earth’s surface above where the earthquake starts is called the

A. focusB. epicenterC. seismic waveD. starting point

8. Earthquakes are caused mostly by

A. the movement of tectonic platesB. huge explosionsC. strong windsD. landslides

9. Vibrations caused by the movement of rocks during an earthquake are called

A. faultsB. seismographsC. seismic wavesD. epicenters

10. Hot spots

A. move across tectonic platesB. remain stationary while a tectonic plate moves over top of itC. occur only beneath oceansD. occur only on continents

Short Answer1. In your own words, define what a fault is. ______________________________

______________________________________________________________________________________________________________________________________

2. Magma is formed when one of three things happens to melt the rock in the asthenosphere inside the Earth. What are these three things?

______________________________________________________________________

______________________________________________________________________

______________________________________________________________________



WHAT ARE SEISMIC WAVES?There are two main types of seismic waves; body waves and surface waves. BODY WAVES are waves that travel through the underground. There are two types of body waves caused by earthquakes: primary and secondary.

Primary waves, or P-waves, are compression waves; they cause the ground to compress and stretch like a spring along the path of the wave. P-waves can travel through solids, liquids and gases, and are the fastest moving of the seismic waves, moving at about 6 km/s through the Earth’s crust. They can pass through all the different layers of the Earth.

Secondary waves, or S-waves, are also known as shear waves. S-waves move more slowly than P-waves, about 3.5

km/s, and can only travel through solid rock They cannot travel through the Earth’s liquid core. They cause the ground to compress and stretch perpendicular to the direction of the wave. S-waves usually cause more structural damage than P-waves do because S-waves are larger.

SURFACE WAVES travel along the surface of the earth. The type of surface wave caused by earthquakes is called an L-wave.L-waves cause the most destruction. L-waves roll along the Earth’s surface like ripples in a pond. These waves travel more slowly than both P- and S-waves, and only The Learning Centres page 39 of 42

L-waves are a surface wave that rolls along the Earth’s surface like ripples on a pond.

S-waves move like a rope being shaken up-and-down; they cause the ground to compress and stretch perpendicular to the direction of the wave.

P-waves move like a “slinky”; they cause the ground to compress and stretch like a spring along the path of the wave.

Science 10 Plate Tectonics UNIT 1travel a few hundred kilometres from the epicenter.

Measuring EarthquakesA seismograph is an instrument that detects and measures earthquakes. A seismograph can even measure very small tremors that people cannot feel. It makes a record of the movements in the Earth’s crust on a piece of paper. The record is called a seismogram. It provides information about when the earthquake occurred, how long it lasted, and the amount of ground shaking. It is a trace on a piece of paper that looks like wavy lines. The higher the wavy lines are on the seismogram, the stronger the earthquake.

These traces show a series of seismograms for an earthquake felt on Vancouver Island and the Lower Mainland in 2001. It is easy to see that the closer the seismograph was to the earthquake, the larger the trace of P- and S-waves. Scientists use the time difference in arrival between the P- and S-waves to determine how far away the earthquake was.

The most common earthquake scale used is the Richter Scale, which is a measure of the magnitude or energy released during an earthquake. Magnitude is a number that rates the strength (or energy) of an earthquake. Higher magnitudes indicate larger earthquakes. With each 1-step increase in magnitude, the energy released by the earthquake is approximately 32 times larger. Thus, an earthquake of magnitude 4.0 is about 1024 (32x32) times greater in energy than an earthquake of magnitude 2.0.

WHAT ARE SEISMIC WAVES? - questionsMultiple Choice



1. _______________ are seismic waves that travel through solids, liquids, and gases.

A. S-wavesB. P-wavesC. L-wavesD. G-waves

2. ______________ are seismic waves that travel through solids only.


3. The first seismic waves to be recorded by a seismograph are the


(Hint: the fastest waves will arrive at the seismograph first).

4. The last seismic waves to be recorded by a seismograph are the


5. The slowest moving waves are the


6. The earthquake waves that cause the most damage are the


Science 10 Plate Tectonics UNIT 1A. S-wavesB. P-wavesC. L-wavesD. G-waves

7. The waves known as surface waves are the


8. The instrument used to detect and measure earthquakes is called a

A. seismologistB. voltmeterC. earthquake meterD. seismograph

9. The scale used to measure the magnitude and energy of an earthquake is the

A. temperature scaleB. bathroom scaleC. Richter scaleD. seismograph scale

Match the wave name with the direction of wave movement.

9. ____ P-waves rolls like ripples on a pond

10.____ S-waves compress and stretch perpendicular to the wave direction

11.____ L-waves compress & stretch like a spring


what are the layers of the earth’s interior … · web viewcontinental crust is the land on which...

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