2What is Plate Tectonics? Scientists know that Earth’s surface consists of a number of rigid, yet movable, pieces called plates.The study of the formation and movement of these plates is called plate tectonics.There are about a dozen major plates and several minor plates.
5These major plates are free of charge on page 5 of your ESRT These major plates are free of charge on page 5 of your ESRT. We will learn this page later this week.
6About the PlatesTogether, the crust and mantle of the Earth make up a single solid layer called the lithosphere.The lithosphere is rigid, but broken up into these plates that move.It is approximately 100 km thick.Recall, there are two types of crust: oceanic and continental.
7About the Plates Which type of igneous rock makes up oceanic crust? Yes, that’s right! BasaltWhich type of igneous rock makes up continental crust?You got it! GraniteWhich one is more dense?You’re brilliant! It’s basalt. Of course, remember, we can go to page 10 of our ESRT and get that info for free!
9About the PlatesThe lithosphere rests on a layer in the mantle called the asthenosphere.This layer is partially melted, thus, it’s what causes the plates in the lithosphere to move!Guess what it is in the asthenosphere that forces the movement of the plates?Our old friend… Convection Currents!!
10About the PlatesWhere convection currents are rising, it will push apart 2 plates!!Where convection currents are sinking, it will pull 2 plates together!!Convection current animation
11This is also free of charge on page 10 of your ESRT!!
12Evidences For Plate Tectonics There are 4 major pieces of evidence that support the theory of plate tectonics:1. Africa and South America2. Magnetism of Seafloor3. Earthquakes and Volcanoes4. Heat Flow and Seafloor Elevation
13Evidences for Plate Tectonics Africa and South AmericaThere is a remarkable similarity in the shape of the west coast of Africa and the east coast of South America.They look like they fit together like puzzle pieces.This suggest that they were once together.This theory is called the continental drift theory.Alfred Wegener was the scientist who proposed this theory.
14Evidences For Plate Tectonics Wegener also noted that the fossil remains of the Mesosaurus were only found in 2 places:1. West coast of Africa2. East coast of South AmericaThis further supported his theory.The name for the large land mass that was all the continents together is known as Pangaea.
15Evidences For Plate Tectonics Pangea Breakup Animation
17Evidences For Plate Tectonics Magnetism of SeafloorSome igneous rocks contain magnetic minerals.These minerals will align themselves towards Earth’s poles.When we look at the bottom of the ocean floor, we see a banding pattern of magnetic minerals in the rocks.They are aligned one way for a chunk of time and then reversed the other way.
18Evidences For Plate Tectonics This suggests that Earth’s poles have reversed in the past.These bands allow scientist to date the rocks of the ocean floor.The youngest rocks are found at the spreading center, where new rock is being formed.The oldest rocks are found along the coasts of the continents.This proves that the plates have been moving for millions of years.
19Evidences For Plate Tectonics (Normal)(Reversed)
20Age of seafloor by magnetic stripes Fig. 3-12Age of seafloor by magnetic stripes
21Evidences For Plate Tectonics Earthquakes and VolcanoesIt has been long observed that earthquakes and volcanoes DO NOT occur randomly on Earth’s surface.Instead, they tend to occur in specific belts.These belts just happen to be location of the boundaries between the plates.These boundaries are so active that stress builds up and causes earthquakes.In addition, the boundaries are areas of extreme heat flow, causing volcanoes.
23Location of earthquakes – each black dot is an earthquake
24Evidences For Plate Tectonics Heat Flow and Seafloor ElevationHeat flow at plate boundaries provides evidence of convection currents in the asthenosphere.Heat flow is highest at a spreading center, where two plates are moving apart.At this center, the seafloor is elevated because the heated materials are expanding.These elevated centers create ocean ridges. The most well-known is the Mid-Atlantic Ocean Ridge.
26Types of Plate Boundaries There are 3 main types of plate boundaries:1. Divergent2. Convergent3. Transform
27Types of Plate Boundaries 1. Divergent BoundariesAlso known as spreading centers.2 lithospheric plates are moving APART (diverging).Most are found on the seafloor, forming ocean ridges.Because of this, some of the world’s oceans are getting bigger!Ocean ridges have valleys called rift valleys.The rift valleys are broken into fracture zones.These are the sources of earthquakes.
29Types of Plate Boundaries 2. Convergent Boundaries2 tectonic plates are moving TOGETHER. (converging)Three types of convergent boundaries:1. Ocean-Ocean crust convergence2. Ocean-Continental crust convergence3. Continental-Continental crust convergence
30Types of Plate Boundaries Ocean-Ocean Convergence and Ocean-Continental Convergence:2 oceanic plates coming together or 1 ocean plate and one continental plate coming together.One plate will be pushed under the other (the MORE dense one gets pushed under).This is called subduction.Subduction creates trenches.The subducted plate melts and this will form volcanoes or island arcs (volcanic islands).
32Types of Plate Boundaries Continental-Continental Convergence:2 continental plates are coming together.When they collide, NO subduction occurs because continental crust is not very dense and one will not subduct another.Instead, the crust gets crumpled and uplifted and often creates mountain ranges.The most famous is the Himalayas when India collided with Eurasia.
34Types of Plate Boundaries 3. Transform Boundaries:2 plates SLIDE past each other.Crust will be deformed and fractured due to the friction and stress.This will create faults and cause earthquakes at these boundaries.Most famous transform fault is the San Andreas Fault in California.
35San Andreas Fault Picture San Andreas Fault animation