Plate Tectonics Evolution of the Earth Free powerpoints at :

Plate TectonicsPlate TectonicsEvolution of the Earth

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How do we know anything about the Earth

How do we know anything about the Earth

• Interior structure

• Volcanoes and hotspots

• Earthquakes

• Tectonic plates

• Tectonic motion

• Reconstruction of the Earth’s history

• Interior structure

• Volcanoes and hotspots

• Earthquakes

• Tectonic plates

• Tectonic motion

• Reconstruction of the Earth’s history

InteriorInterior

InteriorInterior

What’s in the Earth’s Layers:Crust: is made up of Silicates

Mantle: -Lithosphere: upper part of the mantle and the

earht’s crust made up cooler-rigid rock.

-Asthenosphere: middle part of mantle made up softer weaker rock that can flow slowly.

-Mesosphere: stiffer rock that goes to the core.

Core:-Outer core: liquid metal and very hot!

-Inner core: solid metal and very high pressure!

VolcanoesVolcanoes• Volcanoes are the result of hot spots within

the crust or mantle of the earth.• The hot, liquid rock will break through weak

spots in the surface and form volcanoes or flood basalts.

• Many volcanoes do not release lava, instead they spit ash and small bits of lava called lapilli.

• Some eruptions are quiet with very fluid (low viscosity (flow) ) lava flows while others are explosive

VolcanoesVolcanoes

Quiet lava flows

VolcanoesVolcanoes

Mt. St. Helen before the explosive eruption

VolcanoesVolcanoes

VolcanoesVolcanoesTime lapse of the eruption

VolcanoesVolcanoes

Mt. St. Helen after the eruption

VolcanoesVolcanoes

Mt. St. Helens begins the rebuilding process

VolcanoesVolcanoes

Shield Volcanoes: produce when low-vicosity lava makes a wide flat volcano.

Flood basalts: When volcanic eruptions coats a thick layer of magma

over the surface of the earth.

Flood basalts: When volcanic eruptions coats a thick layer of magma

over the surface of the earth.

VolcanoesVolcanoes

Flood basaltsFlood basaltsBasalt is a type of rock that is produced from the mantleBasalt is a type of rock that is produced from the mantle

Magma is always moving in the earth’s mantle due to

Convection: Hot materials rising and cool materials

sinking. This causes the plates to 1) move apart (Divergent Boundaries) or

2) move together (Convergent Boundaries) and even

3) past one another (Transform Boundaries.)

Because Plates move they cause the magma to be released through volcanoes of various types and sizes.

Volcano locations:Why at these locations?

Volcano locations:Why at these locations?

The reason volcanoes occur at specific locations:

1. Plate Tectonics Move at a Subduction (Convergent) Zone:

• Convergent Zones: Volcanoes


2. At Divergent Zones:


3. Magma moves to the surface of the earth near a weak spot and can activate a magma chamber

• http://sio.ucsd.edu/volcano/about/magma.html4. This can happen over a HOTSPOT. The Hawaiian Islandshave formed because a platemoved over a hotspot.

http://sio.ucsd.edu/volcano/about/magma.html

Different Forms of Energy In the Earth

• Mechanical Energy: Energy due to motion

• Heat energy: energy due to heat

• Potential energy: energy that is built up but not yet released

• Kinetic Energy: energy that is occurring (in motion)

What types of energy are taking place to have a volcano?

• Mechanical Energy: – Magma moves from the interior earth up to a weak

portion in the earth’s crust.– Magma also moves out from the volcano. – Ash and rock can also move out from a volcano

like in a pyroclastic flow.

• Heat Energy– The earth’s core has large amounts of heat that

escape at the earth’s surface through a volcano

Draw how a volcano works by using words to describe the process such as: magma, crust, mantle, mechanical energy, heat energy

EarthquakesEarthquakes• Earthquakes are a result of motion within

the earth.

• This only occurs where the earth is solid and therefore can only occur within about 100 miles of the surface

• Earthquakes provide the best evidence regarding the interior structure of the Earth.

EarthquakesEarthquakes




Types of seismic waveThere are two types of seismic wave,

namely, 'body wave' and 'surface wave'

• Body waves travel through the interior of the Earth. They follow raypaths bent by the varying density and stiffness of the Earth's interior.

• Surface waves are similar to water waves and travel just under the Earth's surface. They travel more slowly than body waves. Because of their low frequency, long duration, and large amplitude, they can be the most destructive type of seismic wave.

http://www.answers.com/topic/density

http://www.answers.com/topic/surface-wave

Body Waves and Surface waves fall under two categories:

1) P-Waves: occurs when fault moves past each other horizontally, cause a compressed wave.

2) S-Waves: occurs when faults move vertically, causes a wavy wave.

Both Body Waves and

Surface Waves will

differ in both S & P

Waves:

http://www.answers.com/topic/pswaves-jpg-1

Seismograph: Measures movement in the earth.

Seismograph: Measures movement in the earth.

Finding an Earthquake’s EpicenterFinding an Earthquake’s Epicenter

http://www.seis.utah.edu/../req2webdir/recenteqs/index_map.map

http://www.seis.utah.edu/../req2webdir/recenteqs/index_map.map

http://www.quake.utah.edu/recenteqs/Maps/112-42.map


Tidal waves or Tsunamis result when a large section of the sea floor suddenly moves and therefore displaces a massive amount of water.

Tidal waves or Tsunamis result when the low amplitude long wavelength waves reach the shallow shoreline and begin to feel the bottom of the sea floor. This Shortens the wavelength and increase the amplitude (height).


Location of worldwide earthquakes


Earthquakes by depth.Notice that the deep earthquakes occur only at subduction zones.

Based on MotionBased on Motion

• It turns out that the upper section of the mantle is adhered (stuck to the underside side of the crust to form what we call tectonic plates

Tectonic PlatesTectonic Plates


Today plate boundaries are determined by examining the location of volcanoes and earthquakes.

Volcanoes result from the friction (heat) of the platesmotion.

Earthquakes occur where plate rub against one another


Our first evidence of tectonic motion is based on similar fossils and rock types on opposing sides of the ocean


Tectonic PlatesTectonic PlatesEarthquakes

Tectonic PlatesTectonic PlatesVolcanoes





Another source of evidence is based on seafloor ages which get younger as we approach sea floor ridges


Our final piece of evidence is the magnetic record of the ocean floor.

This shows the pattern of reversal and we find a near perfect mirror image on opposing sides of the ridge




Composition vs. MotionComposition vs. Motion

We can look at the interior of the Earth based on the composition of the rocks or based on the movement

Based on CompositionBased on Composition

• Crust – solid, relatively low density silicate rock• Mantle – Semi fluid, denser, mafic (iron and

magnesium bearing) rocks• Core – Liquid then solid iron and nickel with traces of

heavier elements

Plate TypesPlate Types• Oceanic plates: basalt

– Dark (black) and dense rock type composed of silicates, iron and magnesium

• Continental plates – granite and andesite– Light colored (pink, white

and gray) and low density rock type composed almost entirely of silicates.

Plate BoundariesPlate Boundaries• Convergent – plates move toward

one another

• Divergent – plates move away from each other

• Transform – plate moves sideways from each other

Faults occur at these Plate boundaries, where land masses move. These faults when moved release energy in the form

of an earthquake.There are 3 different faults:

1. Normal Fault: as stress is pulled away on the plates, one land mass slips down. (Divergent Plate boundary)

2. Reverse Fault: as two plates come together one land mass jets up above the other making a hanging wall. (Convergent Plate Boundary)

3. Transverse Fault: occurs as two plates slide past one another. (Transform plate boundary)

Plate BoundariesPlate Boundaries

Plate BoundariesPlate Boundaries

Convergent PlatesConvergent Plates



Convergent PlatesConvergent PlatesThe only subduction zone in the AtlanticThe only subduction zone in the Atlantic


Black arrows show subduction zones and the direction of plate movement


Looking at the depthof earthquakes showsthat angle that the plate is being subducted

Divergent PlatesDivergent Plates




Transform PlatesTransform Plates

Transform PlatesTransform Plates

San Andreas Fault

Mid-Plate HotspotsMid-Plate Hotspots




Why do the Plates Move?Why do the Plates Move?

Why do the Plates Move?Why do the Plates Move?• No single idea explains everything but we can

identify several forces that contribute to the movement of the plates.– Slab pull

• The sinking of the cooled dense oceanic plates pulls on the rest of the plate

– Ridge rises• The material deposited on the top of the ridge slides downs

from the rise pushing on the plate

– Convection• Movement within the mantle could be part of the driving force

behind the motion of the plates.

The Big PictureThe Big Picture

Pangea• What is Pangaea? • Pangaea was a super continent at one time.• Scientists use the similarity of rock types and fossil types that date

to the same age to support their theory that the continents were connected to form a super continent.

• The map below give just one example of areas on different continents that show the same fossils and rock types.

PangeaPangea

PangeaPangea

PangeaPangea

The break up of Pangea

Where are we going?Where are we going?

We appear to be headed for another super continent as North America,

South America, Asia and Australia converge in the ever shrinking Pacific Ocean

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