Presentation on theme: "Plate Tectonics THE RESTLESS EARTH Learning Objectives"— Presentation transcript:
1Plate Tectonics THE RESTLESS EARTH Learning Objectives To Understand the structure of the earth through a fully labelled diagramTo know the distribution of plates and the difference between continental and oceanic platesDescribe and explain what happens at each of the different plate boundaries
3How old is the Earth? The Earth is… 2 million years old
4(figures are in ‘million years ago’) History of the EarthMark the following events on your time line.What do you notice?First flowers appear – 100 mIndia collides with Asia – 50 mMan (Homo sapiens) inhabits the Earth – 0.1 mFormation of the Alps – 30 mYou were born! – mDinosaur extinction – 65 mIndustrial Revolution (UK) m(figures are in ‘million years ago’)4,6004,0003,0002,0001,000todaymillion years ago
5History of the EarthPeople (Homo sapiens) only appeared 100,000 years ago!While all care is taken to ensure web links contain useful information, Boardworks does not take responsibility for the content or accuracy of external web sites.4.6 billion years ago: Earth is formed, along with the other planets4.2 billion years ago : Continents begin to form3.7 billion years ago: Earth's crust solidifies3.5 billion years ago: First life appears in oceans3.25 billion years ago: Photosynthesis begins in oceans2.4 billion years ago: Oceans contain significant amounts of oxygen1.9 billion years ago: First cells with nuclei appear in oceans0.65 billion years ago: First multicellular organisms appear0.5 billion years ago: First land plants with inner vessels245 million years ago: Age of Dinosaurs begins150 million years ago: Supercontinent breaking up; continents drifting apart65 million years ago: Age of Dinosaurs ends, with mass extinction of 70% of all living things3.5 million years ago: First proto-humans appear, in what is now Africa100,000 years ago: First Homo sapiens appear10,000 years ago: Recorded human history beginsBig Bang!Dinosaursdie outMen-like apesHomo sapiens
8The Structure of the Earth Crust- thin skin of cool rockCore- a ball of solid iron and nickel. It is surrounded by a large mass of semi- molten rock, which moves very slowly called the mantle.
9The Earth’s surface (crust) is divided into tectonic plates The crust is not one continuous layer but is made up of seven large tectonic plates and many smaller ones (slabs of rock floating on the mantle).
11Why do the plates move? Crust Convention Currents Mantle The Earth’s crust is unstable because the plates are moving in response to rising hot currents called convection currents within the mantle. The movement of the plates has greatest impact, where two tectonic plates meet. The centre of the plates away from the margins, tend to be stable and distant from major tectonic activity.
16There are two types of tectonic plates (crust) Continental plates (crust)- which is lighter (less dense), thicker about 30km or more, and mostly above sea levelOceanic plates (crust)- which is heavier (more dense), thinner about 5km, and mostly below sea level.The movement of the plates has greatest impact, where two tectonic plates meet, known asa plate boundary or margin. The centre of the plates away from the margins, tend to be stable and distant from major tectonic activity.
17EarthquakesEarthquakes occur in long narrow bands, mainly along plate boundaries at all 3 types: destructive, constructive and conservativeE.g. of earthquakes at a destructive boundary with Nazca plate being subducted under the South AmericanOccur in linear clustersOccur on the land and in the seaLargest belt runs around the Pacific Ocean where there is clustering around the edge of the Pacific plateOther major belts travel along the middle of the Atlantic Ocean and through the continents of Europe and Asia from the Atlantic to the Pacific Ocean
18Distribution of earthquakes and volcanoes Volcanoes occur in long, narrow bandsMany volcanoes are found around the Pacific Ocean e.g. Pacific Ring of FireThere is a line of volcanoes running down the middle of the Atlantic OceanThere are no volcanoes in AustraliaVolcanoes are found both on the land and in the seaFound at constructive and destructive boundariesNearly all the volcanoes on the land are sited close to the oceans
22Name the tectonic plate on which Australia is located on Figure 4b 2) Describe the distribution of active volcanoes on Figure 4b (3 marks)
23Name the tectonic plate on which Australia is located on Figure 4b Indo-Australian plate2) Describe the distribution of active volcanoes on Figure 4b (3 marks)• in a ring around the Pacific• on plate boundaries• odd ones not on plate boundary• clusters on the margins of continents• none in Australia
24Explain why the global distribution of volcanoes is so uneven (3)
25Uneven because they occur at plate boundaries (1), plate boundaries are linear hence lines of volcanoes(1), plate boundaries often close to continentalmargins (1), destructive margins (1), constructivemargins in mid-ocean (1).
26There are three different types of plate movement: Some plates move towards each other (convergent or destructive) e.g. Nazca and South American platesSome plates move away from each other (divergent or constructive) e.g. Nazca and Pacific plates.Some plates slide past each other (conservative or transform) e.g. Pacific and North American plate.The plates meet at plate boundaries or plate margins, which are areas of great crustal stress. These meeting points are where most of the world’s earthquakes and volcanoes and other structural features, such as fold mountains, rift valleys and ocean trenches.
27Constructive plate boundary At a constructive plate boundary, two plates move apart. As the two plates move apart, magma rises up to fill the gap. This causes volcanoes. However, since the magma can escape easily at the surface the volcano does not erupt with much force.Earthquakes are also found at constructive boundaries.An example of a constructive boundary is the Mid-Atlantic Ridge.
29Constructive plate boundary At a constructive plate boundary, two plates move apart. As the two plates move apart, magma rises up to fill the gap. This causes volcanoes. However, since the magma can escape easily at the surface the volcano does not erupt with much force.Earthquakes are also found at constructive boundaries.An example of a constructive boundary is the Mid-Atlantic Ridge.
30Constructive marginsTwo (continental) plates moving apart as a result of convection current in the Earth’s crust that determine the direction of movement. Some plates like the North American and Eurasian plates, are moving in opposite directions, away from each other. This type of movement mostly happens under the oceans. As the plates move apart, the ‘gap’ is filled by magma rising up from the mantle below, and plugs the gap and cools and creates new crust. As this occurs again and again, layers of lava solidify to create volcanoes. The rising magma creates shield volcanoes which, if they become high enough, form volcanic islands, such as Iceland. So much magma poured out that the ridges are built up from the sea bed, like the Mid-Atlantic ridge, upon which Iceland is located.
31Mid-Atlantic ridge Sea Floor Spreading! Did you know that the ocean floor in the Atlantic is growing by 3cm per year?Which of the following pairs of continents are moving further away from each other?Europe and AfricaEurope and North AmericaSouth America and North America
32How fast do plates move? Tectonic plates move at different rates. The Nazca and Pacific plates are moving apart at a rate of 18cm per year while the Eurasian and North American plates are moving apart at a rate of 3cm per year.To the nearest metre, how far will the Nazca and Pacific plates have moved over the next 200 years?6 metres36 metres928 metres200 metres
33Constructive plate boundaries mid-ocean ridgeAoceanBoceanic crustmantleWhere would you find older rocks – at A or at B?
34Destructive plate boundary A destructive plate boundary is found where a continental plate meets an oceanic plate.The oceanic plate descends under the continental plate because it is denser. As the plate descends it starts to melt due to the friction caused by the movement between the plates. This melted plate is now hot, liquid rock (magma). The magma rises through the gaps in the continental plate. If it reaches the surface, the liquid rock forms a volcano.
35Destructive margins are where two plates move towards each other e. g Destructive margins are where two plates move towards each other e.g. along the West Coast of Japan.Where an oceanic plate e.g. Nazca meets a continental plate e.g. South American plate the Nazca plate is forced to sink below the South American plate because it is denser. The oceanic crust sinks into the subduction zone, forming an oceanic trench. Energy builds up in the subduction zone- at certain times this may be released as an earthquake. The molten rock called magma, may rise upwards, causing volcanic eruptions and leading to the creation of composite volcanoes.The lighter continental crust stays at the surface but sediment becomes crumpled into fold mountains. The Andes are the fold mountains that have formed along the West Coast of South America.
39Collision plate boundary Collision boundaries occur when two plates of similar densities move together (i.e. a continental plate and a continental plate). This causes the material between them to buckle and rise up, forming fold mountains.The Himalayas are an example of a chain of fold mountains. They have been formed by the African plate colliding into the Eurasian plate.
41Conservative plate boundary Conservative plate boundaries exist where two plates do not directly collide but slide past each other along a fault (weakness).No volcanoes are found along these plate boundaries, but earthquakes do occur.An example of such a boundary is the San Andreas Fault in California.
43Conservative plate margins Conservative margins are where two plates are moving sideways past each other, or are moving in the same direction but at different speeds.At the San Andreas fault in California, the North American plate and the Pacific plate are sliding past each other. They are moving in the same direction but the North American plate is moving slightly faster. Pressure builds up along the fault until one plate jerks past each other, causing an earthquake. The movement has also caused the land to become ridged and crumpled. (see image below)The San Andreas fault, which passes through San Francisco Bay where 7 million people live