Plate tectonics is that the model or theory that has been used for the past sixty years to know Earth’s development and structure additional specifically the origins of continents and oceans, of pleated rocks and mountain ranges, of earthquakes and volcanoes, and of geological phenomenon. it's explained in some detail in Chapter ten, however is introduced here as a result of it includes ideas that area unit necessary to several of the topics coated within the next few chapters.
Key to understanding morphology is Associate in Nursing understanding of Earth’s internal structure, that is illustrated in Figure. Earth’s core consists largely of iron. The inner core, though even hotter, is beneath most pressure that it's solid. The mantle is created of iron and metallic element salt minerals. the majority of the mantle, encompassing the outer core, is solid rock, however is plastic enough to be able to flow slowly. encompassing that a part of the mantle could be a partly melted layer (the asthenosphere), and therefore the outer a part of the mantle is rigid. The crust composed largely of granite on the continents and largely of volcanic rock below the oceans is additionally rigid. The crust and outer rigid mantle along structure the geosphere. The geosphere is split into concerning twenty tectonic plates that move in numerous directions on Earth’s surface.
An important property of Earth (and alternative planets) is that the temperature will increase with depth, from near to 0°C at the surface to concerning 7000°C at the centre of the core. within the crust, the speed of temperature increase is concerning 30°C/km. this is often called the energy gradient.
Heat is ceaselessly flowing outward from Earth’s interior, and therefore the transfer of warmth from the core to the mantle causes convection within the mantle. This convection is that the primary actuation for the movement of tectonic plates. At places wherever convection currents within the mantle area unit moving upward, new geosphere forms (at ocean ridges) and therefore the plates move apart (diverge). wherever 2 plates area unit connexion (and the convective flow is downward), one plate are subducted (pushed down) into the mantle below the opposite. several of Earth’s major earthquakes and volcanoes area unit related to focused boundaries.