The Structure of the Earth and Plate TectonicsStructure of the EarthThe Earth is made up of 3 main layers:CoreMantleCrustInner coreOuter coreMantleCrustThe CrustThis is where we live!The Earths crust is made of:Continental Crust thick (10-70km)- buoyant (less dense than oceanic crust) - mostly oldOceanic Crust- thin (7 km)- dense (sinks under continental crust)- youngHow do we know what the Earth is made of?Geophysical surveys: seismic, gravity, magnetics, electrical, geodesyAcquisition: land, air, sea and satelliteGeological surveys: fieldwork, boreholes, minesWhat is Plate Tectonics?If you look at a map of the world, you may notice that some of the continents could fit together like pieces of a puzzle.Plate TectonicsThe Earths crust is divided into 12 major plates which are moved in various directions.This plate motion causes them to collide, pull apart, or scrape against each other.Each type of interaction causes a characteristic set of Earth structures or “tectonic features.The word, tectonic, refers to the deformation of the crust as a consequence of plate interaction.World PlatesWhat are tectonic plates made of?Plates are made of rigid lithosphere.The lithosphere is made up of the crust and the upper part of the mantle.What lies beneath the tectonic plates?Below the lithosphere (which makes up the tectonic plates) is the asthenosphere.Plate Movement“Plates of lithosphere are moved around by the underlying hot mantle convection cellsPractical Exercise 1Supercontinents!What happens at tectonic plate boundaries?DivergentConvergentTransformThree types of plate boundarySpreading ridgesAs plates move apart new material is erupted to fill the gapDivergent BoundariesAge of Oceanic CrustCourtesy of ngdc.noaa.govIceland has a divergent plate boundary running through its middleIceland: An example of continental riftingThere are three styles of convergent plate boundariesContinent-continent collisionContinent-oceanic crust collisionOcean-ocean collisionConvergent BoundariesForms mountains, e.g. European Alps, HimalayasContinent-Continent CollisionHimalayasCalled SUBDUCTIONContinent-Oceanic Crust CollisionOceanic lithosphere subducts underneath the continental lithosphereOceanic lithosphere heats and dehydrates as it subsides The melt rises forming volcanismE.g. The AndesSubductionWhen two oceanic plates collide, one runs over the other which causes it to sink into the mantle forming a subduction zone. The subducting plate is bent downward to form a very deep depression in the ocean floor called a trench. The worlds deepest parts of the ocean are found along trenches. E.g. The Mariana Trench is 11 km deep!Ocean-Ocean Plate CollisionWhere plates slide past each otherTransform BoundariesAbove: View of the San Andreas transform faultPractical Exercise 2Where will the UK be in:1,000 years?1,000,000 years?1,000,000,000 years?whats the connection?Volcanoes and Plate TectonicsVolcanism is mostly focused at plate marginsPacific Ring of Fire- Subduction - Rifting - HotspotsVolcanoes are formed by:Pacific Ring of FireHotspot volcanoesHot mantle plumes breaching the surface in the middle of a tectonic plateWhat are Hotspot Volcanoes?Photo: Tom Pfeiffer / volcanodiscoveryThe Hawaiian island chain are examples of hotspot volcanoes.The tectonic plate moves over a fixed hotspot forming a chain of volcanoes.The volcanoes get younger from one end to the other.whats the connection?Earthquakes and Plate TectonicsAs with volcanoes, earthquakes are not randomly distributed over the globeAt the boundaries between plates, friction causes them to stick together. When built up energy causes them to break, earthquakes occur.Figure showing the distribution of earthquakes around the globeWhere do earthquakes form? Figure showing the tectonic setting of earthquakesPlate Tectonics SummaryThe Earth is made up of 3 main layers (core, mantle, crust)On the surface of the Earth are tectonic plates that slowly move around the globePlates are made of crust and upper mantle (lithosphere)There are 2 types of plateThere are 3 types of plate boundariesVolcanoes and Earthquakes are closely linked to the margins of the tectonic plates