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In this section we will examine the classification

of rocks.

The rock cycle.

The evidence for plate tectonics.

And the plate tectonics movement and how it's classified.

In this rock cycle there are three classifications

of rocks.

Igneous sedimentary and metamorphic.

Igneous rock is formed when liquid magma coming up

out of the volcano's calls into a solid.

This rock creates new mountains.

Once these mountains cool the external he drives the

climate changes that cause weathering and erosion.

That begins the breaking down and tearing down of the mountains.

Wind water and ice break down the rocked of the

mountains and then move it away eventually moving it

towards and into the oceans.

These particles are deposited in layers as sediment

that over overtime turn into sedimentary rock.

Finally the sedimentary rocks get pushed down into

deeper levels and under high pressure and high

temperature are changed into metamorphic rock.

Eventually metamorphic rocks are pushed even

deeper until they are melted and turned into magma

and the cycle starts again.

Earlier i talked about the tectonic plates in the lithosphere.

These plates have been identified and plotted on

this map.

This is the african played as you can see.

It extends far out into the atlantic ocean.

It is bigger than just the land mass of the continent.

We are sitting on the arabian plate.

In the early days before the plate tectonic theory

was proposed by doctor wenger.

Geologists were busy mapping the locations of

volcanoes and earthquakes.

Over time their developed a pattern that generally

trace the plate boundaries of today.

Also they began to collect other data that propose

that all of the contents might have been one at one time.

Two hundred and fifty million years ago geologist

believe the continent's were together as one.

The five major pieces of evidence to support this

theory are as follows.

First the present day continents seem to fit

together if you trace their movement backwards in time.

South america fits into africa and north america

fits into europe.

Second many of the mountain ranges on different

continents have the same types of rocks.

A good example is the appalachian mountains in north

america are very similar to the ural mountains in europe.

This indicates that they were formed before the

break up of the supercontinent.

Third there are three hundred and four hundred

million year old fossils and have been discovered.

When these animals and plants died they were

captured in the layers of sediment and in time turned

into iraq.

For example when we examine these rocks closely we

see many of the same fossils in south america and

south africa.

Signifying that at one time they must have been

together before the continental drift began.

Next there is also subsurface evidence that

sections of different continents show exactly the

same ancient climates in the rock records.

Hundreds of millions of years ago.

Places that were hot or dry or wet are exactly the same.

Again where the land mass would have been joined

before the drift began.

And the fifth piece of evidence is one seen on the

ocean floor in magnetic stripes.

In this animation you can see what geologist think is

going on.

It has been observed that on the bottom of the ocean

their a stripes who's magnetic field alternate

between north and south.

In the center here this volcanic activity is spewing

hot lava that flows outward filling in gaps as the

continent's drift apart usually at the margins of

the plates.

This lava is full of iron.

As the iron ions cool down the adams align themselves

with the earth's magnetic field.

With all irons pointing in the same direction.

Now for some reason as scientists still don't know

why every six hundred thousand years or so the

earth's magnetic field changes direction.

From north to south or from south to north.

On the bottom of the ocean you can observe the stripes.

You can measure how these lava flows overtime

changed magnetic direction.

One strip will be magnetized in one direction and the

next in op's direction creating stripes.

You can create the same event in laboratory by making

a magnet.

Take a piece of iron and heated until it is very hot and

molten red hot.

Almost liquid.

As it starts to cool down put a magnet next to it.

The iron molecule is a polar molecule it as a plus side

and a minor side said all the minor ends and the plus

ends of.

Each molecule start lining up.

According to the magnetic field.

All these molecules will line up in a certain

direction because they are hot and they are still liquid.

They can move and eventually they turn into a solid

and their eyes become fixed in position fixed in the

same direction.

A can't change.

They stay that way and become a magnet.

You can do the same with hot rock that is full of iron.

They found that rock will become magnetic as it cools.

It will have a direction.

Like i said earlier the magnetic field changes about

every six hundred thousand years or so if you take a compass.

One stripe will cause the needle to move north and in

the next stripe the needle will reverse itself and

point south.

We don't know why they magnetic field keeps changing

but we still use our powers of observation to

describe and record now let's talk about the earth's surface.

It's crust.

We will look at how the crossed as ever changing how it

is dynamic.

We will describe the theory of how new crust is made.

An old crust is destroyed.

We have identified three types of played movement at

the margins which is another word for edge or boundary.

The three types of played movements are divergent

convergent and transform.

The first type of plate movement is divergent.

In this animation you can see how the two plates are

moving apart.

They are moving in opposite directions.

In this movement ridges are created by volcanic

activity that spews from the gaps.

When these plates move apart creating riffs or holes.

It is here where new crust is created.

The second type of player movement is called convergent.

In this played movement the two plates color lied.

They pushed together until the side with the higher

density is pushed down and under.

And the lighter side is pushed up.

The plate that moves up becomes mountain forming and

the plate that moves down continues.

I'm down.

Until metamorphic rock is formed.

And then if pushed even further down it has

transformed into hot magma.

It is here where the crust is destroyed.

The third type of plate movement is called transform.

In this movement the two plates merely move from side

to side sideways in a lateral movement.

This movement neither creates or destroys crust.

This movement moves the plates back and forth

causing violent earthquakes.

Now let's look at some specific geological examples.

On this map we see symbols that the geologist used to

show plate boundary movement.

They are divergent.

Convergence.

And transform.

Using these symbols to read the map.

We can see that the arabian plate located between

africa and the eurasian plate.

Is moving away from africa and toward asia.

As the arabian played moves away from africa.

This riff the red sea has been formed.

This is divergent movement.

New crust is formed when these two plates are moving apart.

We also have the rift valley.

The east african rift valley has lots of long thin

places with volcanic activity.

Slowly moving apart it will eventually form an

african see here and a new plate will begin to form

here where the arabian played is moving into the

eurasian played.

We have convergent movement.

As the arabian played moves into and under the

eurasian plate the plate is slowly moving under or ron.

Producing the tsar goes mountains which are being

built as the aeration plate is lifted.

The arabian played slips under the asian plate and

all crossed will be destroyed creating a trench.

One thing to note.

Oceanic plates because of their denser composition

of iron are pushed down.

Light continental crust made of silicates is pushed

up in all cases.

The dancer plate whether oceanic crust against

continental crust or ca don't know crust against

continental crust is pushed down.

Remember in divergent the plate boundaries are

moving a part in convergent.

They're moving together pushing into each other.

In transform.

The plate slide past each other in a sideways movement.

Here is another example of convergent plate movement.

One plate pushing against another.

The indian continent is moving.

It is a separate plate.

The indian plate is slowly being pushed down under

the eurasian plate.

Indian crust is being destroyed while the eurasian

crust is being lifted creating the himalayan mountains.

The indian played movement is a good example of subduction.

In a subduction zone the area where the played that is

being pushed down.

There is a lot of friction as the rockslides against

other rocks.

It gets so hot it starts to melt forming metamorphic rock.

Then as it is pushed deeper down metamorphic rock is

destroyed and melted and changed into magma.

Some of this magma flows out of volcanoes creating

new mountains.

In the subduction zone we also see a trench forming

here and mountains being created.

Here.

Mountain building and cross destruction happen at

convergent plate boundaries.

The plate that is pushed down then starts to fuel

volcanic activity.

Using the crust from subduction that eventually

turns to magma that will be used to build new mountains.

This is part of a cycle.

That geologist call the rock cycle.

Here is an example of transform margins.

The arabian played is moving this way see the arrows.

They tell you that the boundaries are moving in the

opposite direction.

The gulf of aqaba was formed by transform played movement.

It goes up through lebanon and into turkey.

You can see these valleys.

It is an earthquake zone.

To review there are three types of played movement

had played.

Margins are boundaries.

Divergent which causes the pledge to move in the

opposite direction.

This creates hold on the cross that is filled in by

volcanic activity creating new crust.

Convergent which pushes the to played margins

together causing one side to be lifted making the

mountains and the others to be pushed down in to the

subduction zone that destroys crust.

Transform causes the played margins to move sideways.

This is where you get violent earthquakes but crust

is neither created nor destroyed.