Lis Sowerbutts in Geology BasicsThe Basics The world is a dynamic place, the earth that we stand on, and think of as fixed, is anything but. Along with the destruction though, comes the creation of many of the mineral deposits we rely on. Plate tectonics is the theory that explains why there are lots of volcanoes in Iceland and Japan, but far fewer in Russia and Africa. It also explains why the Himalayas are the highest mountains in the world while the highest peak in Australia is barely over m!
Plate tectonics has revolutionized virtually every discipline of the Earth sciences since the late s and early s. It has served as a unifying model or paradigm for explaining geologic phenomena that were formerly considered in unrelated fashion. Plate tectonics describes seismic activity,… The theory of plate tectonics is based on a broad synthesis of geologic and geophysical data.
It is now almost universally accepted, and its adoption represents a true scientific revolution, analogous in its consequences to quantum mechanics in physics or the discovery of the genetic code in biology. For details on the specific effects of plate tectonics, see the articles earthquake and volcano.
A detailed treatment of the various land and submarine relief features associated with plate motion is provided in the articles tectonic landform and ocean. Principles of plate tectonics In essence, plate-tectonic theory is elegantly simple.
While the interiors of the plates are presumed to remain essentially undeformed, plate boundaries are the sites of many of the principal processes that shape the terrestrial surface, including earthquakes, volcanismand orogeny that is, formation of mountain ranges. A cross section of Earth's outer layers, from the crust through the lower mantle.
For a deeper discussion of plate-driving mechanisms, see Plate-driving mechanisms and the role of the mantle. Depending on the material they travel through, the waves may either speed up, slow down, bend, or even stop if they cannot penetrate the material they encounter.
Collectively, these studies show that Earth can be internally divided into layers on the basis of either gradual or abrupt variations in chemical and physical properties. Chemically, Earth can be divided into three layers.
A relatively thin crustwhich typically varies from a few kilometres to 40 km about 25 miles in thickness, sits on top of the mantle.
Beneath the mantle is the core, which extends to the centre of Earth, some 6, km nearly 4, miles below the surface. Geologists maintain that the core is made up primarily of metallic iron accompanied by smaller amounts of nickelcobaltand lighter elements, such as carbon and sulfur.
There are two types of crust, continental and oceanicwhich differ in their composition and thickness.
The distribution of these crustal types broadly coincides with the division into continents and ocean basins, although continental shelveswhich are submerged, are underlain by continental crust.
The continents have a crust that is broadly granitic in composition and, with a density of about 2. Continental crust is typically 40 km 25 miles thick, while oceanic crust is much thinner, averaging about 6 km 4 miles in thickness.
These crustal rocks both sit on top of the mantle, which is ultramafic in composition i. The Moho is clearly defined by seismic studies, which detect an acceleration in seismic waves as they pass from the crust into the denser mantle. The boundary between the mantle and the core is also clearly defined by seismic studies, which suggest that the outer part of the core is a liquid.
The four main types of seismic waves are P waves, S waves, Love waves, and Rayleigh waves. The effect of the different densities of lithospheric rock can be seen in the different average elevations of continental and oceanic crust.
The less-dense continental crust has greater buoyancy, causing it to float much higher in the mantle. Its average elevation above sea level is metres 2, feetwhile the average depth of oceanic crust is 3, metres 12, feet. The lithosphere itself includes all the crust as well as the upper part of the mantle i.
However, as temperatures increase with depth, the heat causes mantle rocks to lose their rigidity. This process begins at about km 60 miles below the surface.
This change occurs within the mantle and defines the base of the lithosphere and the top of the asthenosphere. This upper portion of the mantle, which is known as the lithospheric mantle, has an average density of about 3.
The asthenosphere, which sits directly below the lithospheric mantle, is thought to be slightly denser at 3.
In contrast, the rocks in the asthenosphere are weaker, because they are close to their melting temperatures. As a result, seismic waves slow as they enter the asthenosphere.
With increasing depth, however, the greater pressure from the weight of the rocks above causes the mantle to become gradually stronger, and seismic waves increase in velocity, a defining characteristic of the lower mantle.
The lower mantle is more or less solid, but the region is also very hot, and thus the rocks can flow very slowly a process known as creep. During the late 20th and early 21st centuries, scientific understanding of the deep mantle was greatly enhanced by high-resolution seismological studies combined with numerical modeling and laboratory experiments that mimicked conditions near the core-mantle boundary.
At a depth of about 5, km 3, milesthe outer core transitions to the inner core.
The polarity of the iron crystals of the OIC is oriented in a north-south direction, whereas that of the IIC is oriented east-west. Earth's coreThe internal layers of Earth's core, including its two inner cores.
Plate boundaries Lithospheric plates are much thicker than oceanic or continental crust. Their boundaries do not usually coincide with those between oceans and continentsand their behaviour is only partly influenced by whether they carry oceans, continents, or both.
The Pacific Plate, for example, is entirely oceanic, whereas the North American Plate is capped by continental crust in the west the North American continent and by oceanic crust in the east and extends under the Atlantic Ocean as far as the Mid-Atlantic Ridge.Practice test exam 1 study guide by kupuck19 includes 86 questions covering vocabulary, terms and more.
b. mapping of tectonic plate boundaries c. analysis of chemical difference between felsic and mafic rock masses When two oceanic tectonic plates collide, the result is likely to be. Transform boundaries are formed or occur when two plates slide past each other in a sideways motion.
They do not tear or crunch into each other (but the rock in between them may be ground up) and therefore none of the spectacular features are seen such as occur in divergent and convergent boundaries/5(11).
when two plates collide a forms convergent plate boundary when an oceanic plate slide under a continental plate, a deep ocean forms. near the trench, a line of . If two like plates collide, they Depending on the type of plates that collide, they either lift or subduct.
When an oceanic plate collides with a continental plate, it . Physics Unit 5 study guide by clareboord includes questions covering vocabulary, terms and more. a process in which two plates collide and the denser plate is deflected downward beneath the other plate.
two lithospheric plates sliding past one another with no production or destruction of rock. An Analysis of How Any Two Plates Collide. words. 1 page. The Origins of Fire, Its Different Types, and How to Prevent It. words. 1 page. An Analysis of the Substance Calcium in Chemistry and Biology.
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