Chapter 6 Plate Tectonics

Section 1: Inside the Earth

The Composition of the Earth There are two ways that scientists think about the Earth’s layers: 1) By composition 2) By physical properties This includes temperature, density, and ability to flow The Earth is divided into three main layers: 1) The Crust 2) The Mantle 3) The Core The lightest materials make up the outside of the Earth while the heaviest make up the inside

The Crust Crust - is the outermost layer of the Earth It ranges from 5 to 100 km thick It is also the thinnest layer of the Earth Because we live on this layer we know more about this layer than the other two. There are two types of crust: 1) Continental - the crust above the ocean It is made up of mostly granite and has an average thickness of about 30 km 2) Oceanic - the crust under the ocean It is made up of mostly basalt (basalt is denser than granite) and has an average thickness between 5 and 8 km thick

The Mantle Mantle - is the layer of the Earth between the crust and the core The mantle is about 2,900 km thick and contains most of the Earth’s mass No one has ever seen what the mantle really looks like It’s just to deep to drill into In some cases mantle rock has been pushed to the surface by tectonic forces allowing scientists to study mantle rocks Scientists have determined that the composition of the mantle is similar to the mineral olivine, which is a mixture mostly of magnesium and iron

The Core Core - extends from the bottom of the mantle to the center of the Earth. The diameter of the core is about 6,856 km, which is slightly larger than the planet Mars The core contains 33% of the Earth’s mass

The Structure of the Earth

The Structure of the Earth The Earth is divided into 5 main PHYSICAL layers (outside / in): 1) Lithosphere (“rock sphere”)- is the outermost, rigid layer of the Earth. It is made up of the crust and the rigid part of the upper mantle Unlike the other physical layers of the Earth, the lithosphere is not a single solid layer, it is made up of pieces called - tectonic plates 2) Asthenosphere (“weak sphere”) - is a soft layer of the mantle on which the lithosphere moves It is made of a solid rock that moves very slowly like putty These low-strength rocks tend to lose their shape when stressed

3) Mesosphere (“middle sphere”) - is the strong lower part of the mantle beneath the asthenosphere The mesosphere extends from the bottom of the asthenosphere to the Earth’s core 4) Outer Core - is the liquid layer of the Earth’s core that lies beneath the mantle and surrounds the inner core 5) Inner Core - is the solid, dense center of our planet that extends from the bottom of the outer core to the center of the Earth The center of the Earth is 6,378 km beneath the surface

Thicknesses of the Physical Layers 1) Lithosphere: 15 - 300 km 2) Asthenosphere: 250 km 3) Mesosphere: 2,550 km 4) Outer Core: 2,200 km 5) Inner Core: 1,228 km

Tectonic Plates Tectonic Plates - are pieces of the lithosphere that move around on top of the asthenosphere Major Tectonic Plates: 1) Pacific Plate 2) North American Plate 3) Cocos Plate 4) Nazca Plate 5) South American Plate 6) African Plate 7) Eurasian Plate 8) Indian Plate 9) Australian Plate 10) Antarctic Plate

A Giant Jigsaw Puzzle Looking at the previous slide, notice how all of the major tectonic plates fit together like a puzzle. Notice how all of the tectonic plates are not the same For example the North American plate is much larger than the Cocos plate Also the North American plate has an entire continent on it, while the Cocos plate is completely covered by ocean Like the North American plate, some plates include both continental and oceanic crust

A Tectonic Plate Close Up What would a tectonic plate look like if you could lift it out of place? It could consist of only oceanic crust, or only continental crust, or both, like the North and South American plates The thickest part would be where the mountain ranges are, while the thinnest would be under the ocean where ridges are located Remember oceanic crust is much thinner than continental crust Why?????????????????????????????

Mapping the Earth’s Interior How do we know so much about the Earth’s interior when scientists have never even drilled through the Earth’s crust, the thinnest part? The secret lies in Earthquakes When an earthquake occurs it produces vibrations called Seismic Waves Depending on what the material is made of, seismic waves will travel at different speeds For example, they travel faster through solid rock compared to liquids Scientists can measure these waves and their speeds with a Seismograph which allows them to predict the consistency of the Earth’s layers

Chapter 6 Quiz 1 1) ___________ is the outer most layer of the Earth based on composition. 2) ___________ is the outermost rigid layer of the Earth based on physical properties 3) ___________ is the solid, dense portion of the core 4) ___________ are pieces of the lithosphere that move around on the asthenosphere 5) ___________ is beneath the asthenosphere and when translated means “middle sphere” Bonus) _____________ is when two tectonic plates slide past each other.

Section 2- Restless Continents

Wegener Theory of Continental Drift In the early 1900’s Alfred Wegener wrote a book about his theory of continental drift Continental drift - is the theory that continents can drift apart from one another and have done so in the past Does this help explain why the continents could fit together like a puzzle?!?!?!?!?!?!? Does this explain why certain fossil types are found on opposite sides of the Atlantic Ocean?!?!?!?!?!? Look at the following slide. Does continental drift explain these findings? Does continental drift explain why glacier cut grooves in the Earth match up if you put the continents back together?!?!?!?!?!?

The Breakup of Pangaea Wegener studied many observations before establishing his theory He thought that all the separate continents of today were once joined as a single land mass he called -Pangaea Pangaea is Greek for “All Earth” This occurred over 245 million years ago

Sea-Floor Spreading Sea-floor spreading - is the process by which new oceanic lithosphere is created as older materials are pulled away Mid-ocean Ridges are places where sea-floor spreading takes place mid-ocean ridges are chains of underwater mountains that run throughout the world As tectonic plates move away from each other, the sea-floor spreads apart and magma rises up to fill the gap When observing sea-floor spreading, notice that the newest part of the crust is where the spreading occurs and gets older as it gets further away

Magnetic Reversals Some of the most important evidence of sea-floor spreading comes from magnetic reversals recorded in the ocean floor Magnetic Reversal - Is when the magnetic north and south poles change place This has happened many times in Earth’s history Molten rock at mid-ocean ridges contain tiny grains of magnetic minerals These grains act like compasses and align with the magnetic field of the Earth Once cooled these minerals are set in place Scientists consider these as additional evidence that sea-floor spreading occurs

Chapter 6 - Quiz 2 1) ____________ is the theory that continents can drift apart from one another and have done so in the past 2) T/F There are identical fossil types on opposite sides of the Atlantic Ocean 3) ___________ is the name that Wegener came up with do describe all the continents together as a single land mass 4) ___________ are places where sea-floor spreading takes place 5) ___________ is the process by which oceanic lithosphere is created as older materials are pulled away Bonus) __________ is the boundary where two plates meet.

Section 3 - The Theory of Plate Tectonics Plate Tectonics - is the theory that the Earth’s lithosphere is divided into tectonic plates that move around on top of the asthenosphere Because both oceanic and continental crust appear to move, this NEW THEORY was devised to explain both continental drift and sea-floor spreading So what causes tectonic plates to move!?!?!?!?!?!?

Possible Causes of Tectonic Plate Motion It takes an incredible amount of energy to move something as large as a tectonic plate Possible causes include; 1) Slab Pull - is the process by which an oceanic plate slides down and under a continental plate 2) Ridge Push -is the process by which an oceanic plate slides down the slope of the lithosphere/asthenosphere boundary This happens because the ocean lithosphere is higher at mid ocean ridges versus where it gets pushed down under the continental lithosphere 3) Convection - is the process by which hot material from deep within the Earth rises, while cool material near the surface sinks. This forms a circular motion that drags plates sideways away from mid-ocean ridges

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Tectonic Plate Boundaries All tectonic plates have boundaries with other tectonic plates, and are classified into three main types depending on how they move in relation to one another 1) Convergent Boundaries - are when two plates push into each other There are three types of convergent boundaries A) Continental/Continental collisions - are when two plates with continental crust collide This causes the plates to buckle and thicken pushing the continental crust upward These collisions form some of the largest mountains in the world B) Continental/oceanic collisions - is when a plate with continental crust collides with a plate with oceanic crust This causes the oceanic plate (thinner) to slide under the continental plate (thicker) The region where the ocean plate sinks down into the asthenosphere is called a subduction zone C) Oceanic/Oceanic collisions - is when two oceanic plates collide This causes one oceanic plate to slide under the other causing a subduction zone

2) Divergent Boundaries - are when two tectonic plates move away from one another This type of boundary causes sea-floor spreading and mid-ocean ridges These boundaries can also be found on continents Divergent boundaries are where new lithosphere is formed 3) Transform Boundaries - are when two tectonic plates slide past each other The San Andreas fault is an example of a transform boundary This fault marks the location where the Pacific Plate and the North American plate slide past each other This type of boundary can cause EARTHQUAKES !!!!!!!!!!!!! This is because the plates do not slide smoothly past each other. They grind and jerk as they slide past each other

Tracking Tectonic Plate Motion How fast a tectonic plate moves depends on many factors including the type and shape of the plate and how they are interacting with other plates around them Normally plates move very slowly (a few cm per year) Exceptions include transform boundaries like the San Andreas fault, that can move several meters during an Earthquake One way to measure plate movement is with a Global Positioning System (GPS), which measures how far ground stations placed on tectonic plates move, by using a satellite in space

Ch. 6 Quiz 3 1) ____________ is the theory that the Earth’s lithosphere is divided into plates that move on top of the asthenosphere 2) LIST one of the three possible causes of plate movement 3) ___________ boundary is where two tectonic plates push into each other 4) ___________ boundary is where two tectonic plates move away from each other 5) ___________ boundary is where two tectonic plates slide past each other Bonus) _____________ is the name given to the rim of the pacific ocean, because of all the volcanoes and volcanic activity that occurs there.

Section 4 - Deforming the Earth’s Crust Stress - is the amount of force per unit area that is put on a given material The conditions under which a rock is stressed determines its behavior When rock changes shape due to stress, this reaction is called deformation Like a piece of spaghetti, rock can bend or break depending on the type of stress that is placed on them Rocks can deform due to the forces of plate tectonics Compression - is the type of stress that occurs when an object is squeezed This type of stress occurs when two plates collide Convergent boundary compression can cause large mountain ranges to form (i.e. Rocky Mountains)

Folding Folding - occurs when rock layers bend due to stress in the Earths crust When you see a fold in the layers of the Earth’s crust, you know deformation has taken place The two most common folds are anticlines and synclines and form compression Monoclines are a third type of fold that forms an upward or downward force

Faulting While some rock layers bend and fold under stress, some rocks will break Fault - is the surface along which rocks break and slide past each other The blocks of crust on each side of a fault are called fault blocks If a fault is not vertical it is useful to distinguish between the two sides - hanging wall and foot wall

Depending on how the hanging wall and foot wall move relative to each other, two main types of faults can form 1) Normal Fault - causes the hanging wall to move down relative to the footwall This fault normally occurs when rocks move away from each other (divergent)

2) Reverse Fault - causes the hanging wall to move up relative to the footwall Reverse faults usually occur when rocks push together (convergent)

3) Strike-Slip Fault - occurs when opposite forces cause rock to break and move horizontally (transform)

Plate Tectonics and Mountain Building When tectonic plates collide, land features that start out as small folds and faults can eventually become great mountain ranges The reason mountains exist is that tectonic plates are continually moving and bumping into each other Most major mountain ranges form at the edges of tectonic plates Mountains can form in several different ways

2) Fault Block Mountains 1) Folded Mountains Form when rock layers are squeezed together and pushed upward 2) Fault Block Mountains Tectonic forces can place so much force and tension on the Earth’s crust that a large number of normal faults can form in one area When large blocks of the earth’s crust drop down relative to other blocks, fault block mountains are formed

3) Volcanic Mountains Most of the world’s major volcanic mountains are located at convergent boundaries These boundaries often include subduction zones where one plate slips under another and is forced downward These rocks melt and become magma Volcanic mountains form when molten rock erupts onto the Earth’s Surface Unlike folded and fault block mountains, volcanic mountains form from new material being added to the Earth’s surface There are so many volcanic mountains around the rim of the Pacific ocean that early explorers named it the RING OF FIRE !!!!!!

Folded Mountain Fault Block Mountain Volcanic Mountain

Chapter 6 Quiz 4 1) ____________ is the type of stress that is formed when two plates collide 2) ____________ occurs when rock layers bend due to stress 3) ____________ is the type of fault when the hanging wall moves UP compared to the foot wall 4) ____________ is the type of fault when the hanging wall moves DOWN compared to the foot wall 5) ____________ is the type of fault when opposite forces cause rock to break and move horizontally Bonus) List 5 of the 10 major tectonic plates