Chapter 4 Plate Tectonics

Section 1

Lesson Objectives Identify the layers of the earth by composition Identify the layers of the earth by their physical properties Describe Plate Tectonics

Keywords Crust Mantle Core Lithosphere Asthenosphere Mesosphere Tectonic Plates Composition Physical Structure Seismic waves Identify the layers of the earth by composition Identify the layers of the earth by their physical properties Describe Plate Tectonics

Keywords: Composition, Physical Structure Earths Layers: Divided 2 different ways: 1.Composition (What it’s made of) 2.Physical Structure (Ex: solid or liquid) Identify the layers of the earth by composition Identify the layers of the earth by their physical properties Describe Plate Tectonics

Keywords: Crust, Mantle, Core Three layers based on composition: 1. Crust 2. Mantle 3. Core Identify the layers of the earth by composition Identify the layers of the earth by their physical properties Describe Plate Tectonics Note: Denser material collects in the core because denser objects always sink due to gravity.

Keywords: Core Identify the layers of the earth by composition Identify the layers of the earth by their physical properties Describe Plate Tectonics The Core 1. Makes up 33% of the Earth’s mass 2. Mostly Fe with some Ni (the denser elements) 3. Little to No: O, Si, Al & Mg

Keywords: Mantle Identify the layers of the earth by composition Identify the layers of the earth by their physical properties Describe Plate Tectonics The Mantle 1.Between the core and crust 2.Contains most of the Earth’s mass (67%) 3.Mostly Mg & Fe with some Si, O, & Al (more Mg than Al, because Mg is more dense) 4.Temperature = 870 o C – 2200 o C 5.Composition studied from volcanic eruptions

Keywords: Crust Identify the layers of the earth by composition Identify the layers of the earth by their physical properties Describe Plate Tectonics The Crust Thin & solid, outer most layer (5 – 100 km thick) up to 870 o C (increasing with depth) Continental Crust: Often composed of granite; mostly Si, O, Al, Ca, Na, K; thick & less dense Oceanic Crust: Usually composed of basalt; mostly Si, O, Fe, Mg; thin & more dense Why does oceanic crust sit lower than continental crust? Why does oceanic crust sit lower than continental crust?

Keywords: Lithosphere, Asthenosphere, Mesosphere, Outer Core, Inner Core Identify the layers of the earth by composition Identify the layers of the earth by their physical properties Describe Plate Tectonics Physical Structures of the Earth Five layers based on Physical Properties 1.Lithosphere 2.Asthenosphere 3.Mesosphere 4.Outer Core 5.Inner Core

Keywords: Lithosphere, Asthenosphere, Mesosphere Identify the layers of the earth by composition Identify the layers of the earth by their physical properties Describe Plate Tectonics Lithosphere 2 parts: rocky crust and rigid, outermost mantle TECTONIC PLATES!!!! Asthenosphere Plastic (flowing) upper mantle directly beneath the lithosphere Due to heat and pressure Mesosphere Strong, dense lower layer of the mantle

Keywords: Outer Core, Inner Core Identify the layers of the earth by composition Identify the layers of the earth by their physical properties Describe Plate Tectonics Outer Core molten Fe & Ni – produces Earth’s magnetic field Surrounds Inner Core Temperature =  C Less pressure than inner core Inner Core Solid Fe & Ni Temperature = 5000 o C Extreme pressure Why do you think the outer core is liquid, when the inner core is solid?

How do we know about these layers? By the motion of seismic waves

Keywords: Seismic Waves Identify the layers of the earth by composition Identify the layers of the earth by their physical properties Describe Plate Tectonics Mapping the Earth’s Interior When earthquakes occur, seismic waves (vibrations) are sent out in all directions, through the earth. These vibrations reach different places at different times because of the ways the wave bend and change speed as they pass through the earth’s layers

Keywords: Tectonic Plates Identify the layers of the earth by composition Identify the layers of the earth by their physical properties Describe Plate Tectonics Tectonic Plates: Pieces of lithosphere that move around on top of the asthenosphere Major Tectonic (lithospheric) Plates Pacific Plate North American Plate Cocos Plate Nazca Plate South American Plate African Plate Eurasian Platet Indian Plate Australian Plate Anarctic Plate Tectonic plates are constantly moving. The fastest plate moves at 15 centimeters (6 inches) per year while the slowest plates move at less than 2.5 centimeters (1 inch) per year.

Lithospheric Plate Cross Section

1)Both oceanic and continental plates float on top of the asthenosphere, like ice cubes floating in water, because of their… 2)Just like ice cubes, the plates can move around and often bump into each other. 3)Some of the plate sits below the level of the asthenosphere, just like ice displacing water. Lower density The thicker continental crust displaces more of the asthenosphere than oceanic crust.

Section 2

Lesson Objectives Describe Wegner’s theory of continental drift Explain sea- floor spreading and magnetic reversals Describe how new oceanic lithosphere forms at mid- ocean ridges

Keywords: Describe Wegner’s theory of continental drift Explain sea-floor spreading and magnetic reversals Describe how new oceanic lithosphere forms at mid- ocean ridges Continental drift Pangea Sea-floor spreading Mid-ocean ridge Magnetic reversals

Keywords: continental drift, Pangea Describe Wegner’s theory of continental drift Explain sea-floor spreading and magnetic reversals Describe how new oceanic lithosphere forms at mid- ocean ridges  Alfred Wegener Proposed idea of Continental Drift  Continental drift hypothesis Supercontinent called Pangaea (greek for “all earth”) began breaking apart about 200 million years ago Continents broke apart and then "drifted" to present positions (November 1, 1880 – November 1930)

Keywords: continental drift Describe Wegner’s theory of continental drift Explain sea-floor spreading and magnetic reversals Describe how new oceanic lithosphere forms at mid- ocean ridges Evidence of Pangea and continental drift 1.Fossil evidence 2.Glacial scars 3.Coal deposits 4.Mountain rages 5.Paleoclimate

Keywords: Describe Wegner’s theory of continental drift Explain sea-floor spreading and magnetic reversals Describe how new oceanic lithosphere forms at mid- ocean ridges Wegener ’ s matching of mountain ranges on different continents

Paleoclimatic (Ancient Climate) evidence

To Do… Complete reconstructing Pangea activity

Glossopteris

Mesosaurus

Lystrosaurus

Glacial Striations (scars)

Coal Deposits

Mountain Ranges

Pangea split into Laurasia and Gondwana during the Triassic period

Earthquake Activity: Proof the Plates Exist

Earthquake Depths and Locations around the World

Lithospheric Plates of the World

More proof the plates move: Hot spots can create new land New land that is not formed at plate boundaries

Complete Hot Spot Activity

Keywords: continental drift Describe Wegner’s theory of continental drift Explain sea-floor spreading and magnetic reversals Describe how new oceanic lithosphere forms at mid- ocean ridges Why was Wegener’s hypothesis rejected? People couldn’t observe the plates moving The main objection to Wegener's proposal was its inability to provide a correct mechanism In other words, he couldn’t explain HOW and WHY the continents drift. Wegner did not have a good reason for the driving force of movement of the plates. He claimed it was the same forces that influence tides (gravity).

Where was Wegener missing evidence from?

Keywords: sea-floor spreading, mid-ocean ridge, Describe Wegner’s theory of continental drift Explain sea-floor spreading and magnetic reversals Describe how new oceanic lithosphere forms at mid- ocean ridges Mid-ocean ridges Underwater mountain chains Where sea-floor spreading takes place As plates move away from each other, sea floor spreads and magma rises to fill the gap Older crust is farther away from ridge than younger crust is

Sea Floor Spreading mid-ocean ridges rift valley lithospheric plate asthenosphere magma newer less dense crustolder more dense crust

Sea Floor Spreading A rift valley is volcanically active forming new oceanic crust on each side of the valley creating Mid- Ocean Ridges. The new crust pushes the older crust away from the mid-ocean ridge, moving the ocean floor & the continents Ex: Mid-Atlantic Ridge

Keywords: magnetic reversals Describe Wegner’s theory of continental drift Explain sea-floor spreading and magnetic reversals Describe how new oceanic lithosphere forms at mid- ocean ridges Evidence of sea-floor spreading Magnetic reversals When earth’s magnetic poles change North and south magnetic poles have changed many times throughout history Molten rock contains magnetic minerals which align with the poles When molten rock cools, a record of this is laid in the rocks

Magnetic Reversals

Keywords: Subduction Describe Wegner’s theory of continental drift Explain sea-floor spreading and magnetic reversals Describe how new oceanic lithosphere forms at mid- ocean ridges New crust is continuously made. So why is the earth’s crust not getting bigger?

Keywords: Subduction Describe Wegner’s theory of continental drift Explain sea-floor spreading and magnetic reversals Describe how new oceanic lithosphere forms at mid- ocean ridges Subduction Occurs when oceanic crust collides with oceanic or continental crust The older, more dense, oceanic crust plunges back into the mantle at a deep ocean trench. Forms deep ocean trenches & volcanic mountains or island arcs.

Trenches of the World

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Section 3

Lesson Objectives Describe the three types of plate boundaries Describe the three forces that move the plates and the resulting stress Explain how scientists measure the rate of plate movement

Keywords: Describe the three types of plate boundaries Describe the three forces that move the plates and the resulting stress Explain how scientists measure the rate of plate movement Divergent boundary Convergent boundaries Transform boundaries Ridge push Convection Slab pull Stress Tension Compression Shear

Keywords: Divergent boundary Describe the three types of plate boundaries Describe the three forces that move the plates and the resulting stress Explain how scientists measure the rate of plate movement Divergent – plates move apart in opposite directions – Plate material is being created – Creates sea floor spreading in oceanic crust – Can also be continental crust – East Africa Rift Valley is a young divergent boundary – The Red Sea is an older divergent boundary that has filled with water

Keywords: convergent boundary Describe the three types of plate boundaries Describe the three forces that move the plates and the resulting stress Explain how scientists measure the rate of plate movement Convergent – Plates collide together – Plate material is being destroyed – Subduction and mountain building takes place due to convergent boundaries

Oceanic - Continental Subduction Oceanic - Oceanic Subduction Plate Collisions Continental– Continental (No Subduction Mountain Range instead)

Keywords: transform boundary Describe the three types of plate boundaries Describe the three forces that move the plates and the resulting stress Explain how scientists measure the rate of plate movement Transform – Plates slide past each other – San Andreas fault

Motion at Plate Boundaries

Plate Boundary Features

Keywords: ridge push, slab pull, convection Describe the three types of plate boundaries Describe the three forces that move the plates Explain how scientists measure the rate of plate movement What causes the plates to move? Ridge push (occurs at mid-ocean ridges) Oceanic lithosphere is higher than where is sinks into the asthenosphere so plate slides due to gravity Slab pull Parts of the Lithosphere sinks and pulls the rest of faster as it sinks during subduction Convection Density differences cause magma to rise and fall carrying the plates with it

Keywords: stress Describe the three types of plate boundaries Describe the three forces that move the plates and the resulting stress Explain how scientists measure the rate of plate movement Tectonic stresses are those stresses produced by the forces that drive plate tectonics Stress occurs at plate boundaries Stress = force per unit area

Types of stress at plate boundaries Tension: Stress that pulls apart or stretches a body Compression: Stress that squeezes or shortens a body Shear: Stress that pushes parts in opposite directions

Dominant Stress at Boundary Types: Divergent: Tension Convergent: Compression Transform: Shear

To Do Complete Google Earth activity