Chapter 4 Plate Tectonics Earth Science Chapter 4 Plate Tectonics

Evidence from Rock Samples – Direct (you can hold the rocks) Evidence from Seismic Waves – Indirect – speed of waves and their path are studied

Pressure - Increases with depth - weight of rock from above The three main layers of Earth differ in temperature, composition, pressure and size. Temperature – Temperature increases with depth - heat left over from when earth formed + radioactive elements release heat Pressure - Increases with depth - weight of rock from above

The three main layers of Earth are - the crust, the mantle, Earth's Interior The three main layers of Earth are - the crust, the mantle, and the core. Layers of the Earth are similar to the layers in a hardboiled egg!

The Crust Thinner Mostly Basalt (igneous rock) Solid outer rock – includes land and ocean floor, 5km – 40km thick (can be 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 thick Lithosphere – ‘lithos’ = stone (Greek) Rigid Uppermost part of mantle and crust Asthenosphere – ‘asthenes’ = weak Bendable + softer + can flow The Lower Mantle Solid

The Core - 3486 km thick Mostly iron and nickel Outer Core - liquid Inner Core – dense, solid, extreme pressure squeezes iron and nickel so much that they cannot be liquid

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

Structure of the earth – http://www. youtube. com/watch Structure of the earth – http://www.youtube.com/watch?v=3MFr2cC3erk Layers of the earth song – http://www.youtube.com/watch?v=Q9j1xGaxYzY

Convection 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: Radiation Conduction Convection

Radiation Heat is transferred through space No direct contact between heat source and object sunlight, heat around open fire http://www.youtube.com/watch?v=2JZciWtK6vc&safe=active Eureka Radiation 4:02 (2:39)

Conduction Transfers heat by direct contact Matter touching matter Can occur between any state of matter: solid, liquid or gas Metals are good conductors of heat Bad conductors include wood, rubber, glass Example: Heat transfers directly from the element of a stove to a metal pot http://www.youtube.com/watch?v=wV7gzcKegdU&safe=active Eureka Conduction 2:02

Conduction -

Convection heat transfer by the movement of currents within fluids – liquids and gasses. Hotter particles move further apart and rise (less dense) Cooler particles move closer together and fall (more dense) Transfer is therefore vertical (up & down) Caused by differences in temperature and density http://www.youtube.com/watch?v=ON2Y3FEk_UI&safe=active Eureka Convection 2:06

Convection –.

Convection currents are set in motion by – Heating and cooling of a fluid Changes in the density of the fluid Force of gravity

2 1 3

3 2 1 1

Convection Currents in the Earth Happen in the mantle Caused by heat from the core and the mantle Rock in lower mantle is hotter and less dense than rock in upper mantle . Hot rock rises Cools at top mantle sinks back Heats up and rises again

Methods of heat transfer - https://www.wisc-online.com/learn/natural-science/earth-science/sce304/heat-transfer--conduction--convection--radiation http://openhighschoolcourses.org/pluginfile.php/6926/mod_page/content/1/Week_6_Resources/lsps07_int_heattransfer.swf Convection in the earth – http://www.sciencebook.dkonline.com/11.html

Continental Drift C4S3 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

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

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

3. Ancient Climatic Zones – fossils and rocks Spitsbergen – an island in the Arctic Ocean - once had a warm climate – tropical plants found – island was close to the equator about 300 million years ago, then moved South Africa - rocks and sediments left behind by glaciers. Continental drift had moved South Africa away from South Pole

Sea-Floor Spreading C4L4 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 mid-ocean ridge that rises above water

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.

At the mid ocean ridge, a crack develops. Molten material from deep below earth erupts. As it cools, it forms a strip of solid rock in the center of the ridge. When more molten material comes out, it pushes this rock outwards. New strip of rock is formed. This produces basalt – the rock that forms oceanic crust

Sea floor spreading animation – http://earthguide.ucsd.edu/eoc/teachers/t_tectonics/p_seafloorspreading.html

Evidence of Sea-Floor Spreading 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. Molten Material - shape of rocks – only when molten material hardens quickly under water

Magnetic Stripes - patterns in rocks - rocks of ocean floor contains iron as this rock cools, the iron atoms become magnetized and line up in the direction of the earth’s magnetic poles When the magnetic polarity of the earth changes, the new strip shows new polarity When scientists studied rocks on both sides of ridge, they found strips of rocks alternating on each side in the same way

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

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

Ocean floor near a mid-ocean ridge is new and hot – it moves away towards a deep-ocean trench As it moves away, it cools – becomes more dense. Gravity pulls this denser, cooler floor down beneath the trench Ocean floor sinks back into the mantle Giant conveyor belt – material comes up at the ridge, moves across ocean floor, sinks at trench Takes tens of millions of years

Animation of subduction - http://earthguide. ucsd

It takes 200 million years for new rock to form at mid-ocean ridge, move across ocean, and sink into deep-ocean trench Pacific Ocean is shrinking - has many deep ocean trenches at edges of continents - subduction occurs faster than new rock is formed Atlantic Ocean expanding – fewer deep ocean trenches – as ocean floor spreads, pushes continents – has nowhere to go

The Theory of Plate Tectonics 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 Boundaries There 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 https://www.classzone.com/books/earth_science/terc/content/visualizations/es0804/es0804page01.cfm?chapter_no=visualization https://www.youtube.com/watch?v=ZzvDlP6xd9o http://www.wwnorton.com/college/geo/egeo2/content/animations/2_1.htm

Convergent: colliding boundaries Two plates come together Density of the plates decides which one will be on top Oceanic crust is destroyed Three types of collision plates

Two Oceanic Plates Meet at a trench The denser plate sinks (subducts) under the other plate (as the ocean floor undergoes sea floor spreading, it becomes cooler and denser)

Oceanic Continental Plates The denser oceanic plate sinks (subducts) beneath the less dense continental plate

Two Continental Plates Two continental plates collide Neither is more dense so no subduction Forms mountain ranges (example Himalayas)

Transform: sliding boundaries Two plates slip past each other moving in opposite directions Crust is neither created nor destroyed