Plate TectonicsSocial Studies for 10th E.G.B.Teacher: Mauricio Torres
ConceptIt is a scientific theory that describes the large-scale motions of Earths lithosphere. The theorybuilds on the concepts of continental drift,developed during the first decades of the 20thcentury.
How it worksThe lithosphere is broken up into tectonicplates. On Earth, there are seven or eight majorplates (depending on how they are defined) andmany minor plates. Where plates meet, theirrelative motion determines the type of boundary.Earthquakes, volcanic activity, mountain-building, and oceanic trench formation occuralong these plate boundaries.The outer layers of the Earth are divided intolithosphere (outer) and asthenosphere (inner).
How do they move?Tectonic plates are able to move because theEarths lithosphere has a higher strength andlower density than the underlying asthenosphere.Mechanically, the lithosphere is cooler and morerigid, while the asthenosphere is hotter and flowsmore easily. Therefore, in simpler terms: The key principle of plate tectonics is that the lithosphere exists as separate and distinct tectonic plates, which ride on the fluid-like asthenosphere.
Why do they move?Plate tectonics is basically a kinematic phenomenon:Earth scientists agree upon the observation anddeduction that the plates have moved one withrespect to the other, and debate and find agreementson how and when. But still a major question remainson what the motor behind this movement is; thegeodynamic mechanism, and here science divergesin different theories.One of the theories says: different forces generatedby the rotation of the globe and tidal forces of the Sunand the Moon. The relative importance of each ofthese factors is unclear, and is still subject to debate.
Who thought of this?In 1912 the meteorologist AlfredWegener amply described what hecalled continental drift. Continental drift is the movement of the Earth’s continents relative to each other.Starting from the idea (also expressed by hisforerunners) that the present continents onceformed a single land mass (which wascalled Pangea later on) that drifted apart, thusreleasing the continents from the Earths mantleand likening them to "icebergs" of lowdensity granite floating on a sea of denser basalt.
Formation and break-up of continents The movement of plates has caused the formation and break-up of continents over time, including occasional formation of a supercontinent that contains most or all of the continents. The supercontinent Columbia or Nuna formed during a period of 2,000 to 1,800 million years ago and broke up about 1,500 to 1,300 million years ago. This pieces later re-assembled into another supercontinent called Pangaea; Pangaea broke up into Laurasia (which became North America and Eurasia) and Gondwana (which became the remaining continents).
Plate BoundariesThe location where two plates meet is calleda plate boundary, and plate boundaries arecommonly associated with geological eventssuch as earthquakes and the creation oftopographic features such as mountains,volcanoes, mid-ocean ridges, and oceanictrenches. The majority of the worlds activevolcanoes occur along plate boundaries, with thePacific Plate’s Ring of Fire being most activeand most widely known.
Plate BoundariesBoundaries on the surface and underneath the ocean:
Divergent BoundariesDivergent boundaries (Constructive) occur where twoplates slide apart from each other. Active zones of rifting(such as Africas East African Rift) is an example ofdivergent boundaries.
SubductionIn geology, subduction is the process that takesplace at convergent boundaries by which one tectonicplate moves under another tectonic plate, sinking intothe Earths mantle, as the plates converge. Theseregions of mantle downwellings are known as"Subduction Zones". A subduction zone is an areaon Earth where two tectonic plates move towards oneanother and one slides under the other.Rates of subduction are typically measured incentimeters per year, with the average rate ofconvergence being approximately 2 to 8 centimetersper year (about the rate a fingernail grows).
EffectsThe strains caused by plate convergence insubduction zones cause earthquakes.Nine out of the ten largest earthquakes to occurin the last 100 years were subduction zoneevents. This includes the 1960 Great ChileanEarthquake (which at 9.5 was the largestearthquake ever recorded), the 2004 IndianOcean earthquake and tsunami, and the 2011Tōhoku earthquake and tsunami.
Hot SpotsThe places knownas hotspots or hot spots ingeology are volcanic regionsthought to be fed b underlyingmantle that is anomalously hotcompared with the mantleelsewhere. They may beon, near to, or far fromtectonic plate boundaries.
Hot SpotsHawaii, Réunion, Yellowstone, Galápagos,and Iceland are some ofthe most currently activevolcanic regions to whichthe hypothesis is applied. Pinnacle Rock, Galápagos Islands
Group WorkGet together in groups of five and research on thefollowing sites: Hawaii, Réunion, Yellowstone, Galápagos, or Iceland.First, look up what they have in common. Then youmay have a better idea of what you need to researchon.You will have to prepare an oral presentation of fiveminutes with multimedia.Remember, it must all be related with GEOLOGY.You have two weeks to have it ready.Only the best and most outstanding presentation inthe class, will have a 20 as a final grade on theproject.
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