Earth ScienceEarth Science

Chapter 4 Chapter 4 Plate Plate

TectonicsTectonics

Evidence from Rock Evidence from Rock SamplesSamples – – Direct (you can hold Direct (you can hold the rocks)the rocks)

Evidence from Seismic Evidence from Seismic Waves Waves – – Indirect – speed of waves Indirect – speed of waves and their path are studiedand their path are studied

The three main layers of Earth differ in The three main layers of Earth differ in temperature, composition, pressure temperature, composition, pressure and size.and size.

Temperature – Temperature – Temperature Temperature increases with depth - heat left over increases with depth - heat left over from when earth formed + radioactive from when earth formed + radioactive elements release heatelements release heat

Pressure - Pressure - Increases with depth - Increases with depth - weight of rock from aboveweight of rock from above

Earth's InteriorEarth's InteriorThe three main layers of The three main layers of Earth are -Earth are -the the crustcrust,,the the mantlemantle, , and the and the corecore..Layers of the Earth are similar to the layers in a hardboiled egg!

The CrustThe Crust Solid outer rock – includes land and Solid outer rock – includes land and

ocean floor, 5km – 40km thick (can be ocean floor, 5km – 40km thick (can be 70km beneath mountains)70km beneath mountains)

Oceanic Crust•Thinner•Mostly Basalt (igneous rock)•Denser than continental crust

Continental Crust•Thicker•Mostly Granite (igneous rock)•Less dense than oceanic crust

The Mantle – 3000km thickThe Mantle – 3000km thickLithosphere – Lithosphere – ‘‘lithos’ lithos’ = stone (Greek) = stone (Greek)100 km thick100 km thickRigidRigidUppermost part of mantle and crustUppermost part of mantle and crust

Asthenosphere –Asthenosphere –‘‘asthenes’ = weakasthenes’ = weakBendable + softer + can flowBendable + softer + can flow

The Lower MantleThe Lower MantleSolidSolid

The Core - 3486 km thickThe Core - 3486 km thickMostly iron and nickelMostly iron and nickel

Outer Core - Outer Core - liquidliquid

Inner Core – Inner Core – dense, solid, extreme dense, solid, extreme pressure squeezes iron and nickel so pressure squeezes iron and nickel so much that they cannot be liquidmuch that they cannot be liquid

Earth’s Magnetic FieldEarth’s Magnetic Field

Movements in the earth’s liquid outer Movements in the earth’s liquid outer core create a magnetic field. This core create a magnetic field. This magnetic field surrounds the planetmagnetic field surrounds the planet

Structure of the earth – Structure of the earth – http://www.youtube.com/watch?v=3MFr2cC3erk

Layers of the earth song –Layers of the earth song –

http://www.youtube.com/watch?v=Q9j1xGaxYzY

Convection and the Mantle 4.2Convection and the Mantle 4.2

The movement of energy form a warmer object to a colder object is called Heat Transfer.

There are three types of heat transfer: RadiationConductionConvection

RadiationRadiationHeat is transferred through Heat is transferred through

spacespaceNo direct contact between heat

source and objectsunlight, heat around open fire

http://www.youtube.com/watch?v=2JZciWtK6vc&safe=active

Eureka Radiation 4:02 (2:39)Eureka Radiation 4:02 (2:39)

ConductionConduction Transfers heat by direct Transfers heat by direct contact contact Matter Matter touchingtouching matter matter Can occur between any state of matter: Can occur between any state of matter:

solid, liquid or gassolid, liquid or gas Metals are good conductors of Metals are good conductors of heatheat Bad conductors include wood, rubber, Bad conductors include wood, rubber,

glassglass Example: Heat transfers directly from the Example: Heat transfers directly from the

element of a stove to a metal potelement of a stove to a metal pot

http://www.youtube.com/watch?v=wV7gzcKegdU&safe=active http://www.youtube.com/watch?v=wV7gzcKegdU&safe=active Eureka Conduction 2:02Eureka Conduction 2:02

Conduction -Conduction -

ConvectionConvection heat transfer by the movement of heat transfer by the movement of

currents within fluids – liquids and currents within fluids – liquids and gasses. gasses.

Hotter particles move further apart and Hotter particles move further apart and rise rise (less dense)(less dense)

Cooler particles move closer together Cooler particles move closer together and and fall fall (more dense)(more dense)

Transfer is therefore vertical (up & Transfer is therefore vertical (up & down)down)

Caused by differences in Caused by differences in temperaturetemperature andand densitydensity

http://www.youtube.com/watch?v=ON2Y3FEk_UI&safe=active Eureka Convection 2:06http://www.youtube.com/watch?v=ON2Y3FEk_UI&safe=active Eureka Convection 2:06

ConvectionConvection –. –.

Convection currents are set in Convection currents are set in motion by –motion by –

1.1.Heating and cooling of a fluidHeating and cooling of a fluid

2.2.Changes in the density of the Changes in the density of the fluidfluid

3.3.Force of gravityForce of gravity

2

3

1

1

2

3

1

Convection Currents in the Convection Currents in the EarthEarth

Happen in the mantleHappen in the mantle

Caused by heat from the core and the Caused by heat from the core and the mantlemantle

Rock in lower mantle is hotter and less Rock in lower mantle is hotter and less dense than rock in upper mantle . dense than rock in upper mantle .

Hot rock rises Cools at top mantle Hot rock rises Cools at top mantle sinks back sinks back Heats up and rises againHeats up and rises again

Methods of heat transfer -Methods of heat transfer -https://www.wisc-online.com/learn/https://www.wisc-online.com/learn/natural-science/earth-science/sce304/heat-natural-science/earth-science/sce304/heat-transfer--conduction--convection--radiationtransfer--conduction--convection--radiation

http://openhighschoolcourses.org/http://openhighschoolcourses.org/pluginfile.php/6926/mod_page/content/1/pluginfile.php/6926/mod_page/content/1/Week_6_Resources/Week_6_Resources/lsps07_int_heattransfer.swflsps07_int_heattransfer.swf

Convection in the earth –Convection in the earth –

http://www.sciencebook.dkonline.com/http://www.sciencebook.dkonline.com/11.html11.html

Wegener's hypothesis was that all the continents were once joined together in a single landmass - Pangaea - and have since drifted apart.

Alfred Wegener

Pangaea – the super continent

Continental Drift C4S3Continental Drift C4S3

Evidence of Continental DriftEvidence of Continental DriftEvidence from Land Features 1. Continents fit together like the pieces to a 1. Continents fit together like the pieces to a puzzlepuzzle 2. Mountain ranges 2. Mountain ranges on Africa and South America line upon Africa and South America line up 3. 3. EuropeanEuropean coal fields line coal fields line up with North American up with North American coal coal

fields.fields.

2. Fossil evidence of dinosaurs and prehistoric plants – Glossopteris, Mesosaurus, Lystrosaurus

3. 3. Ancient Climatic Zones Ancient Climatic Zones – – fossils and fossils and rocksrocks

a.a.Spitsbergen – Spitsbergen – an island in the Arctic an island in the Arctic Ocean - once had a warm climate – Ocean - once had a warm climate – tropical plants found – island was close tropical plants found – island was close to the equator about 300 million years to the equator about 300 million years ago, then movedago, then moved

b.b.South Africa - South Africa - rocks and sediments rocks and sediments left behind by glaciers. Continental drift left behind by glaciers. Continental drift had moved South Africa away from had moved South Africa away from South PoleSouth Pole

The longest chain of mountains in the world is the system of mid-ocean ridges – explored with sonar and deep diving vessels (Hess WWII)Iceland is a part of the Iceland is a part of the mid-ocean ridge that rises mid-ocean ridge that rises above waterabove water

Sea-Floor Spreading C4L4Sea-Floor Spreading C4L4

In sea-floor spreading, the sea floor spreads apart along both sides of a mid-ocean ridge as new crust is added. As a result, the ocean floors move like conveyor belts, carrying the continents along with them.

1.1. At the mid ocean ridge, a crack At the mid ocean ridge, a crack develops.develops.

2.2. Molten material from deep below Molten material from deep below earth erupts.earth erupts.

3.3. As it cools, it forms a strip of solid As it cools, it forms a strip of solid rock in the center of the ridge.rock in the center of the ridge.

4.4. When more molten material comes When more molten material comes out, it pushes this rock outwards.out, it pushes this rock outwards.

5.5. New strip of rock is formed.New strip of rock is formed.

6.6. This produces basalt – the rock that This produces basalt – the rock that forms oceanic crustforms oceanic crust

Sea floor spreading animation – Sea floor spreading animation – http://earthguide.ucsd.edu/eoc/http://earthguide.ucsd.edu/eoc/

teachers/t_tectonics/teachers/t_tectonics/p_seafloorspreading.htmlp_seafloorspreading.html

Evidence of Sea-Floor Evidence of Sea-Floor SpreadingSpreading

Evidence supported the theory of sea-floor spreading: eruptions of molten material, magnetic stripes in the rock of the ocean floor, and the ages of the rocks themselves.

1.1.Molten Material - Molten Material - shape of shape of rocks – only when molten material rocks – only when molten material hardens quickly under waterhardens quickly under water

Magnetic Stripes - Magnetic Stripes - patterns in rocks - patterns in rocks -

a.a.rocks of ocean floor contains ironrocks of ocean floor contains iron

b.b.as this rock cools, the iron atoms as this rock cools, the iron atoms become magnetized and line up in the become magnetized and line up in the direction of the earth’s magnetic polesdirection of the earth’s magnetic poles

c.c.When the magnetic polarity of the When the magnetic polarity of the earth changes, the new strip shows earth changes, the new strip shows new polaritynew polarity

d.d.When scientists studied rocks on both When scientists studied rocks on both sides of ridge, they found strips of rocks sides of ridge, they found strips of rocks alternating on each side in the same alternating on each side in the same wayway

3. Drilling Samples – 3. Drilling Samples – age of age of rocks – the youngest rock was at rocks – the youngest rock was at the center of the ridge, the older the center of the ridge, the older rocks were farther away. The rocks were farther away. The farther away from the ridge the farther away from the ridge the rocks were taken, the older they rocks were taken, the older they were.were.

SubductionSubductionDeep Ocean Trenches – deep under water Deep Ocean Trenches – deep under water canyon where ocean floor sinkscanyon where ocean floor sinks

1.1. Ocean floor near a mid-ocean ridge is Ocean floor near a mid-ocean ridge is new and hotnew and hot – it moves away towards a – it moves away towards a deep-ocean trenchdeep-ocean trench

2.2. As it moves away, it As it moves away, it coolscools – becomes – becomes more dense. more dense.

3.3. Gravity pulls this denser, cooler floor Gravity pulls this denser, cooler floor down beneath the trenchdown beneath the trench

4.4. Ocean floor Ocean floor sinkssinks back into the mantle back into the mantle

5.5. Giant conveyor belt – material comes up Giant conveyor belt – material comes up at the ridge, moves across ocean floor, at the ridge, moves across ocean floor, sinks at trenchsinks at trench

6.6. Takes tens of millions of yearsTakes tens of millions of years

Animation of subduction - Animation of subduction - http://earthguide.ucsd.edu/eoc/teachers/t_thttp://earthguide.ucsd.edu/eoc/teachers/t_tectonics/p_subduction.htmlectonics/p_subduction.html

http://education.nationalgeographic.com/http://education.nationalgeographic.com/education/encyclopedia/ocean-trench/?education/encyclopedia/ocean-trench/?ar_a=1ar_a=1

It takes It takes 200 million years 200 million years for new rock to for new rock to form at mid-ocean ridge, move across form at mid-ocean ridge, move across ocean, and sink into deep-ocean trenchocean, and sink into deep-ocean trench

Pacific Ocean is shrinking Pacific Ocean is shrinking - has many deep - has many deep ocean trenches at edges of continents - ocean trenches at edges of continents - subduction occurs faster than new rock is subduction occurs faster than new rock is formedformed

Atlantic Ocean expanding Atlantic Ocean expanding – fewer deep – fewer deep ocean trenches – as ocean floor spreads, ocean trenches – as ocean floor spreads, pushes continents – has nowhere to gopushes continents – has nowhere to go

The Theory of Plate The Theory of Plate TectonicsTectonics

• Pieces of the lithosphere are in slow, constant motion driven by convection currents in the mantle

• It explains the formation, movement, and subduction of Earth's plates (cracks in the lithosphere)

• Convection currents in the mantle cause plate motion

Plate BoundariesPlate BoundariesThere are three kinds of plate

boundaries:

Divergent: spreading boundaries

Convergent: colliding boundaries

Transform: sliding boundaries.

Divergent: Spreading Boundaries

• Two plates move apart

• Can be found at mid ocean ridges where sea floor spreading happens (Ocean floor)

• Spreading boundaries on land produce rift valleys example Great Rift Valley -

in East Africa (deep crack in the African continent)• Oceanic crust is created

• https://www.classzone.com/books/earth_science/terc/content/visualizations/es0804/https://www.classzone.com/books/earth_science/terc/content/visualizations/es0804/es0804page01.cfm?chapter_no=visualizationes0804page01.cfm?chapter_no=visualization

• https://www.youtube.com/watch?v=ZzvDlP6xd9ohttps://www.youtube.com/watch?v=ZzvDlP6xd9o• http://www.wwnorton.com/college/geo/egeo2/content/animations/2_1.htmhttp://www.wwnorton.com/college/geo/egeo2/content/animations/2_1.htm

Convergent: colliding boundaries Two plates come togetherTwo plates come together Density of the plates decides which one Density of the plates decides which one

will be on topwill be on top Oceanic crust is destroyedOceanic crust is destroyed Three types of collision platesThree types of collision plates

Two Oceanic PlatesTwo Oceanic Plates Meet at a trenchMeet at a trench The denser plate sinks (subducts) under The denser plate sinks (subducts) under

the other plate (as the ocean floor the other plate (as the ocean floor undergoes sea floor spreading, it undergoes sea floor spreading, it becomes cooler and denser)becomes cooler and denser)

Oceanic Continental PlatesOceanic Continental PlatesThe denser oceanic plate sinks (subducts) The denser oceanic plate sinks (subducts) beneath the less dense continental platebeneath the less dense continental plate

Two Continental PlatesTwo Continental Plates Two continental plates collideTwo continental plates collide Neither is more dense so no Neither is more dense so no

subductionsubduction Forms mountain ranges (example Forms mountain ranges (example

Himalayas) Himalayas)

Transform: sliding boundaries

Two plates slip past each other moving in opposite directions

Crust is neither created nor destroyed