10/16/2014

Earth Science

Tectonic PlatesPage 194-196

Tectonic plate: a block of lithosphere that consists of the crust and the rigid, outermost layer of the mantle.

Tectonic plates are part of what layer of the Earth?

What layer of the Earth do they move on top of?

The lithosphere is like a giant Earth jigsaw puzzle.

Scientists have named all of the tectonic plates. All of the pieces of tectonic plates fit together. However, not all of the plates are the same.

Look at Figure 4; look at all 10 major tectonic plates. They are all different sizes and include continental and/or oceanic crust.

A Tectonic Plate close up

Figure 5 shows what a plate would look like if you picked it up. What makes up a tectonic plate?

You can think of the tectonic plates on the asthenosphere like a bunch of ice covering a bowl of punch. The ice moves around and pushes other ice out of the way.

Large pieces of ice take up more room and push around more punch than the smaller ice cubes. The ice will also float on the punch.

Tectonic plates behave in the same way. They ‘float’ on the asthenosphere. They all touch each other, but also move each other around.

Thicker plates, those with more continental crust than oceanic crust, are heavier and therefore take up more room and move the asthenosphere more.

Mapping the Earth’s Interior

How can we believe anything we are reading? How do these scientists know what they are talking about?

Most of our answers came from Earthquakes. Earthquakes cause seismic waves. These seismic waves travel through the Earth.

The speed that they can travel depends on the density and composition of material that they are travelling through.

A seismic wave travelling through a solid will go faster than one travelling through liquid.

When we have an earthquake, seismographs are used to measure how quickly the waves travelled. Scientists can then use that data to calculate what the wave was travelling through.

World map

Wegener’s continental drift hypothesis

Alfred Wegener formed the Continental Drift Hypothesis in the 1900s

Continental drift – hypothesis that the continents used to be one large mass, but have broken up to where they are now.

support continental drift hypothesis

Explain how well the continents fit together

Explain why the same animal has fossils on opposite sides of oceans

Similar rock and climate conditions in past same on separate continents

Breakup of pangaea

Wegener named the giant land mass Pangaea which means “all earth”

This would have existed about 245 million years ago

Pangaea split into two continents in 180 million years ago

The two land masses have been named Laurasia and Gondwana

When laurasia and gondwana split, they formed the continents we have today

Sea floor spreading

Wegener’s hypothesis was not supported during his lifetime. People did not believe that something so big as the continents could move.

It was not until many years later that scientists learned how the continents would be able to move

CONTINENTAL DRIFTHomework: read 7.2 + 7.3 for Friday! Plan!

So… What do we know about continental drift??

Who made the hypothesis?

What was his hypothesis?

What was his evidence for it? (4 things)

Wegener named the giant land mass Pangaea which means “all earth”

Pangaea

Breakup of Pangaea

Pangaea would have existed about 245 million years ago

About 180 million years ago, Pangaea split into two continents

The two land masses have been named Laurasia and Gondwana

When Laurasia and Gondwana split, they formed the continents we have today

So… What do we know about Pangaea?

What was it?

What does it’s name mean?

How long ago was it?

What did it split in to?

Wegener never lived to see his hypothesis supported, he never was able to explain why he thought the continents moved.

OK, so how do the continents move?

Sea-Floor Spreading

There is a chain of underwater mountains through the center of the Atlantic Ocean.

This chain is just one part of a world wide system of underwater ridges.

Mid-ocean ridges are underwater mountains where sea-floor spreading happens.

When new oceanic lithosphere forms as magma rises towards the surface and solidifies.

Sea-floor spreading

How does sea-floor spreading work?

As tectonic plates moved apart, magma from the mid-ocean ridges fills the gaps

As the magma cools, it forms the new oceanic lithosphere

Once this new crust forms, it pushes the older crust away from the mid-ocean ridge, forcing the tectonic plates further apart

The process then repeats itself…

- Magnetic Reversals

Good ideas about how plates move… but do we have proof?

Magnetic Reversals

Throughout Earth’s history, the north and south magnetic poles have changed places many times

When those poles change, the north pole has a S magnetic polarity and the south pole has a N magnetic polarity

This change is called Magnetic Reversal

Any guesses?

How does that prove sea-floor spreading?

Proof!!

The molten rock that comes to the surface at the mid-ocean ridge has tiny grains of magnetic minerals in it

The magnetic minerals are made out of iron and act like tiny compasses

When the magma comes to the surface, the magnetic minerals align themselves with the polarity of the Earth

This means…

This means…

This means that when the magma cools and solidifies, the magnetic minerals are still aligned with the polarity of the Earth

When the polarity switches the magnetic minerals that are in cooled magma do not change, but all the new magnetic minerals in the new magma align to the new polarity

This leaves evidence of the past polarity of the Earth

What is going on?

Recap…

Restless Continents

Continental Drift

Breakup of Pangaea

Sea-Floor Spreading

Magnetic Reversal

FINISHING 7.2 AND STARTING 7.3Read 7.2 and 7.3 and take notes for Friday!

Proof!!

The molten rock that comes to the surface at the mid-ocean ridge has tiny grains of magnetic minerals in it

The magnetic minerals are made out of iron and act like tiny compasses

When the magma comes to the surface, the magnetic minerals align themselves with the polarity of the Earth

This means…

This means…

This means that when the magma cools and solidifies, the magnetic minerals are still aligned with the polarity of the Earth

When the polarity switches the magnetic minerals that are in cooled magma do not change, but all the new magnetic minerals in the new magma align to the new polarity

This leaves evidence of the past polarity of the Earth

What is going on?

Recap…

Restless Continents

Continental Drift

Breakup of Pangaea

Sea-Floor Spreading

Magnetic Reversal

SECTION 7.3

Theory of Plate Tectonics

Plate Tectonics

We just learned about how the continents spread apart, but how do those tectonic plates actually move?

There must be a lot of force on those plates to make them move… where does that force come from?

The theory that explains HOW large pieces of the Earth’s outermost crust (tectonic plates) move and change.

Plate Tectonics

Tectonic Plate Boundaries

Before we can learn how the tectonic plates move, we must first learn about how the tectonic plates interact with one another.

A boundary is a place where tectonic plates touch – all tectonic plates share boundaries with other tectonic plates.

The type of boundary depends on how the tectonic plates move relative to one another.

1. Convergent Boundaries2. Divergent Boundaries3. Transform Boundaries

There are 3 different boundaries

1. Convergent Boundaries

The boundary formed when 2 tectonic plates collide

There are 3 different combinations of tectonic plates that can collide 1. 2 continental plates – when these collide

they buckle and thicken, pushing the crust up 2. continental and oceanic plates – then

these collide the oceanic crust is pushed under the continental plate and into the asthenosphere, where it melts.

3. 2 oceanic plates – one plate sinks under the other plate

2. Divergent Boundaries

The boundary when two tectonic plates separate or move apart from one another

The mid-ocean ridges that we learned about yesterday are the most common types of divergent boundaries

When the plates move apart, sea-floor spreading happens

3. Transform Boundary

The boundary that is formed when 2 plates move horizontally or past one another

Because tectonic plates have rough edges, they rub against one another causing earthquakes

The San Andreas Fault in CA is a good example of a transform boundary That is where the Pacific plate and the

North American plate meet

FINISHING 7.3Read 7.2 and 7.3 and take notes for Friday!

What do we know so far?

Plate tectonics is a theory. Lithosphere holds tectonic plates, they move on the asthenosphere

Plate boundaries – there are 3 different ways tectonic plates can meet 1. Convergent boundaries 2. Divergent boundaries 3. Transform boundaries

Why do tectonic plates move? One idea: the solid rock of the asthenosphere

moves very slowly The density of parts of the asthenosphere

changes as they get heated from the rock below. The hotter rocks expand, and therefore become less dense. This causes them to move closer to the surface.

Once they cool, they shrink and become more dense. This causes them to sink down again.

Since tectonic plates rest on the asthenosphere, they move when it moves.

Why do tectonic plates move? Another idea: the lithosphere near mid-

ocean ridges pushes the lithosphere The mid-ocean ridge is higher than the

place where the tectonic plate sinks down into the asthenosphere. Since it is higher, the lithosphere slides down from the ridge to the asthenosphere due to gravity.

Since tectonic plates are on the lithosphere, they move.

Why do tectonic plates move?

Another idea: when the lithosphere sinks into the asthenosphere, the lithosphere layer is much more dense than the asthenosphere.

Just like the other idea, the denser rock is pulled down to the bottom of the asthenosphere. Therefore, the tectonic plate gets pulled deep into the asthenosphere, and starts to pull the rest of the tectonic plate down too.

How fast can tectonic plates move?

The speed depends on how large the tectonic plate is and how it is interacting with the tectonic plates around it.

However, scientists are able to track tectonic plate movements and, on average, they move only centimeters a year.

We cannot see this change since it is so slow.

So how can we measure the speed?

Scientists have GPS systems up in space These systems monitor how far away

certain ground stations are from the GPS.

Scientists are able to see that the ground stations are changing their distance from the GPS. They are able to calculate how fast that is happening over a long period of time, giving us an idea of how fast the plates are moving.

The theory that the lithosphere is divided into tectonic plates that move slowly across the asthenosphere

Plate tectonics?

A few centimeters per year

How fast do tectonic plates move?

What are the 3 ideas about how tectonic plates move?

1. Mid-ocean ridges pushing the lithosphere down into the asthenosphere because of gravity (ridge push)

2. The asthenosphere changing density and moving due to changes in heat (convection)

3. Oceanic plate being pulled down into the asthenosphere because it is denser (slab pull)

It records the distance between the satellite and ground stations. Over time, it calculates the change in the distance.

How do we use GPS to track tectonic plate movement?

CURRENT REVIEW OF CHAPTER 7Take out reading notes from 7.2 and 7.3

Earth Poster

Use as many vocab words as possible to make huge review poster of what we have learned so far

We can make it on the board and you can take a picture of it, or you can make it individually

Vocab words

Crust Mantle Core Lithosphere Asthenosphere Mesosphere Outer Core Inner Core Tectonic Plates

Seismic Waves Continental Drift Alfred Wegener Sea-Floor

Spreading Plate Tectonics Convergent

Boundary Divergent

Boundary

More Vocab Words

Transform Boundary

Ridge Push Convection Slab Pull GPS Continental

Lithosphere

Oceanic Lithosphere

Magnetic Reversal Mesosaurus Pangaea

SECTION 7.4

Write 7.4 vocab for Friday

Deforming the Earth’s crust

Take the popsicle sticks. Slowly and carefully bend it. What happens?

Now take a popsicle stick, bend it quickly and further. Now was happens?

Why do they behave differently? The amount of stress you put on the stick

changes. This same thing happens to rocks, the behaviour changes based on how much stress is put on them

Deformation

Deformation is what happens to the shape of the rock because of stress

Just like the popsicle sticks, rocks can bend or break depending on how much stress is put on the rock

The stress that occurs when forces act to squeeze the object. When this happens to convergent boundaries, mountains can form.

Compression

The stress that occurs when forces act to stretch an object. This generally happens at divergent boundaries when plates pull away from one another.

Tension

Folding

When stresses act on rocks, they cause the rocks to fold.

The bending of rock layers is called folding.

Rocks generally start as horizontal layers, like the three examples, so when we see that they are bent, we know deformation happened.

1. Take at least 5 pieces of paper2. Put water on the paper so it is

damp3. Use your hands to put horizontal

stress on the paper

Do paper experiment

Direction of stress

When horizontal stress in put on the rocks, you tend to see upward-arching folds and downward-arching folds. Do you see any of this with your paper?

When you have vertical stress on the rocks, the rocks shift, but both sides of the rock are still horizontal. Look at the example on the desk, when you put horizontal stress on the rocks, only the middle section changes.

SECTION 7.4

Write 7.4 vocab for Friday

Force on Rocks

Fold the paper in front of you in half Continue the process Count how many times you can fold it in half Does it get more difficult to fold? Why?

With every fold, the amount of paper doubles. After 7 folds there are 128 sheets. The Earth’s crust, like the paper, requires a small amount of pressure to fold the lighter, thin layers. Tremendous amounts of pressure are required to fold over large, denser sections of land.

Faulting

Some rocks break when stress is applied to them. The surface the rocks break along is called a fault. The blocks of crust on either side of the fault are called fault blocks

When the fault is formed, the fault is normally not perfectly vertical, there are 2 different shapes of the fault blocks. Hanging wall and footwall

A break in a body of rock along which one block slides relative to another

Fault

Fault Blocks

Look at the blocks in the front of the room

Which one looks like a footwall? You can use your feet to walk up a footwall

Which one looks like a hanging wall? You would rock climb off of the hanging wall

Types of Faults

The type of fault that forms is determined by how the two fault blocks relate to one another

Types of Faults

Normal Fault The hanging wall

moves down Normally occurs

when the tectonic plates pull rocks apart - tension

Reverse Fault The hanging wall

moves up Normally occurs

when the tectonic plates push rocks together - compression

Telling the difference

You can draw arrows on the picture of the fault blocks to tell which type of faults were formed

You look at the layers of rocks and see which way the hanging rock has moved

Strike-Slip Fault

This is another type of fault This forms when forces cause the rock to

break and move horizontally across each other. You do not have footwalls and hanging walls

These faults do not cause the rocks to move up and down, they cause the rocks to move left and right

SECTION 7.4

Chapter 7 Test Thursday!

Types of mountains

Folded Mountains Highest types of mountains Formed when rocks are squeezed together

are pushed upwards Ex. Appalachian mountains

Fault-Block Mountains Tension causes large normal faults to form Produced sharp, jagged mountains Ex. Tetons mountains

Types of Mountains

Volcanic Mountains Most happen at convergent boundaries Forms when magma rises to the Earth’s

surface and erupts

Uplift

When parts of the Earth’s crust moves up – to higher elevation

Forming mountains is an example of uplift

Can happen when a weight is moved from the crust, and previously depressed rock is now uplifted back to the original position

Subsidence

When parts of the Earth’s crust is moved down – to lower elevation

When rocks cool, they take up less area and subsides to lower elevations. Ex. When the lithosphere cools

This can also happen when the lithosphere is stretched from being on a rift zone. A rift zone is the area between two tectonic plates, when the plates move away, the rock in between the plates sinks.

This is the last part of the chapter, we are having our test on Thursday, does anyone have any questions right now that they are confused about?

Any questions?

Do Stretch Lab

In groups, take a balloon. Draw 3 touching columns on your

deflated balloon Colour in the 2 outside columns Inflate the balloon, what happens to the

drawing? Deflate the balloon, what happens to the

drawing?

Make an Outline

Let’s make an outline of all that we need to know for this test

What vocab words do we need to know? What concepts do we need to know? What would be a good way to remember

them?

SECTION 7.4

Chapter 7 Test Friday

Review Time – pages 190-213 What I want you to do this period is either make

a poster or a few posters of all of the vocab words and main ideas, OR make flashcards about the vocab words and main ideas!

This will help you learn and understand the material better, you will also be able to use what you make for studying.

Also, organize your notes, let me look them over. If you come across anything you do not

understand, ASK ME!