what does the earths interior have to do with plates

Earth's Interior & Plate Tectonics

Copyright © 1995,1996 by Rosanna L. Hamilton. All rights reserved.

A theory is a tool - non a creed. -J. J. Thomson

Table of Contents

• The World'southward Interior
• The Lithosphere & Plate Tectonics
  • Oceanic Lithosphere
  • Continental Lithosphere
  • Plate Tectonics
• References

The Earth'due south Interior

Just as a child may milkshake an unopened present in an attempt to find the contents of a souvenir, then man must mind to the ring and vibration of our Globe in an attempt to discover its content. This is accomplished through seismology, which has become the principle method used in studying World's interior. Seismos is a Greek discussion meaning daze; akin to earthquake, shake, or violently moved. Seismology on Earth deals with the study of vibrations that are produced by earthquakes, the impact of meteorites, or bogus means such equally an explosion. On these occasions, a seismograph is used to measure out and record the actual movements and vibrations within the Earth and of the basis.

Types of seismic waves (GIF, local 15K)
(Adapted from, Beatty, 1990.)

Scientists categorize seismic movements into four types of diagnostic waves that travel at speeds ranging from iii to 15 kilometers (one.ix to 9.iv miles) per second. Two of the waves travel around the surface of the Earth in rolling swells. The other ii, Master (P) or compression waves and Secondary (Due south) or shear waves, penetrate the interior of the Earth. Master waves compress and dilate the matter they travel through (either rock or liquid) similar to sound waves. They also take the ability to movement twice equally fast as S waves. Secondary waves propagate through stone simply are non able to travel through liquid. Both P and S waves refract or reflect at points where layers of differing physical backdrop meet. They also reduce speed when moving through hotter material. These changes in direction and velocity are the means of locating discontinuities.

Divisions in the Earth's Interior (GIF, local 26K)
(Adapted from, Beatty, 1990.)

Seismic discontinuities assist in distinguishing divisions of the World into inner cadre, outer core, D", lower mantle, transition region, upper mantle, and crust (oceanic and continental). Lateral discontinuities also have been distinguished and mapped through seismic tomography merely shall non be discussed here.

• Inner core: 1.7% of the World'south mass; depth of five,150-half dozen,370 kilometers (iii,219 - 3,981 miles)
  The inner core is solid and unattached to the mantle, suspended in the molten outer core. It is believed to have solidified as a outcome of force per unit area-freezing which occurs to near liquids when temperature decreases or pressure increases.
• Outer core: 30.8% of Earth'south mass; depth of 2,890-5,150 kilometers (1,806 - 3,219 miles)
  The outer core is a hot, electrically conducting liquid within which convective motion occurs. This conductive layer combines with Earth's rotation to create a dynamo consequence that maintains a system of electric currents known equally the Globe's magnetic field. Information technology is likewise responsible for the subtle jerking of Earth's rotation. This layer is not as dense as pure molten iron, which indicates the presence of lighter elements. Scientists doubtable that about 10% of the layer is composed of sulfur and/or oxygen because these elements are abundant in the cosmos and dissolve readily in molten fe.
• D": 3% of Earth's mass; depth of 2,700-2,890 kilometers (one,688 - one,806 miles)
  This layer is 200 to 300 kilometers (125 to 188 miles) thick and represents about 4% of the drape-crust mass. Although it is oftentimes identified as office of the lower mantle, seismic discontinuities advise the D" layer might differ chemically from the lower mantle lying above information technology. Scientists conjecture that the material either dissolved in the cadre, or was able to sink through the drape just not into the cadre because of its density.
• Lower curtain: 49.2% of Earth's mass; depth of 650-two,890 kilometers (406 -i,806 miles)
  The lower drapery contains 72.9% of the mantle-crust mass and is probably composed mainly of silicon, magnesium, and oxygen. It probably besides contains some iron, calcium, and aluminum. Scientists make these deductions by assuming the Earth has a like abundance and proportion of catholic elements as institute in the Sun and primitive meteorites.
• Transition region: 7.five% of Globe's mass; depth of 400-650 kilometers (250-406 miles)
  The transition region or mesosphere (for heart mantle), sometimes chosen the fertile layer, contains eleven.1% of the pall-crust mass and is the source of basaltic magmas. Information technology also contains calcium, aluminum, and garnet, which is a complex aluminum-begetting silicate mineral. This layer is dumbo when common cold because of the garnet. Information technology is buoyant when hot because these minerals melt easily to form basalt which tin can then ascent through the upper layers every bit magma.
• Upper drapery: 10.iii% of Earth's mass; depth of 10-400 kilometers (vi - 250 miles)
  The upper mantle contains 15.3% of the pall-crust mass. Fragments have been excavated for our observation by eroded mountain belts and volcanic eruptions. Olivine (Mg,Fe)2SiO4 and pyroxene (Mg,Fe)SiO3 take been the master minerals found in this way. These and other minerals are refractory and crystalline at loftier temperatures; therefore, most settle out of rising magma, either forming new crustal cloth or never leaving the pall. Part of the upper mantle called the asthenosphere might be partially molten.
• Oceanic chaff: 0.099% of Earth'southward mass; depth of 0-10 kilometers (0 - six miles)
  The oceanic chaff contains 0.147% of the drapery-crust mass. The majority of the World's crust was made through volcanic activity. The oceanic ridge arrangement, a forty,000-kilometer (25,000 mile) network of volcanoes, generates new oceanic chaff at the rate of 17 km³ per year, covering the ocean floor with basalt. Hawaii and Iceland are two examples of the accumulation of basalt piles.
• Continental chaff: 0.374% of Earth's mass; depth of 0-50 kilometers (0 - 31 miles).
  The continental crust contains 0.554% of the curtain-chaff mass. This is the outer part of the World composed essentially of crystalline rocks. These are low-density buoyant minerals dominated mostly by quartz (SiO2) and feldspars (metal-poor silicates). The chaff (both oceanic and continental) is the surface of the Globe; every bit such, it is the coldest part of our planet. Because cold rocks deform slowly, we refer to this rigid outer shell as the lithosphere (the rocky or potent layer).

The Lithosphere & Plate Tectonics

Oceanic Lithosphere

The rigid, outermost layer of the World comprising the chaff and upper mantle is called the lithosphere. New oceanic lithosphere forms through volcanism in the form of fissures at mid-ocean ridges which are cracks that encircle the globe. Rut escapes the interior every bit this new lithosphere emerges from below. It gradually cools, contracts and moves away from the ridge, traveling beyond the seafloor to subduction zones in a process called seafloor spreading. In fourth dimension, older lithosphere will thicken and eventually become more than dense than the mantle below, causing it to descend (subduct) back into the World at a steep angle, cooling the interior. Subduction is the main method of cooling the mantle below 100 kilometers (62.5 miles). If the lithosphere is immature and thus hotter at a subduction zone, it volition exist forced back into the interior at a lesser angle.

Continental Lithosphere

The continental lithosphere is about 150 kilometers (93 miles) thick with a low-density crust and upper-mantle that are permanently buoyant. Continents drift laterally along the convecting organization of the mantle away from hot mantle zones toward cooler ones, a process known as continental drift. Most of the continents are at present sitting on or moving toward libation parts of the drapery, with the exception of Africa. Africa was in one case the cadre of Pangaea, a supercontinent that somewhen broke into todays continents. Several hundred million years prior to the formation of Pangaea, the southern continents - Africa, South America, Australia, Antarctica, and India - were assembled together in what is called Gondwana.

Plate Tectonics

Plate tectonics involves the formation, lateral motion, interaction, and destruction of the lithospheric plates. Much of World's internal heat is relieved through this process and many of Earth's large structural and topographic features are consequently formed. Continental rift valleys and vast plateaus of basalt are created at plate break upwards when magma ascends from the drape to the ocean floor, forming new chaff and separating midocean ridges. Plates collide and are destroyed as they descend at subduction zones to produce deep ocean trenches, strings of volcanoes, extensive transform faults, wide linear rises, and folded mountain belts. Globe's lithosphere presently is divided into eight large plates with about ii dozen smaller ones that are globe-trotting in a higher place the mantle at the rate of five to 10 centimeters (2 to 4 inches) per year. The eight large plates are the African, Antarctic, Eurasian, Indian-Australian, Nazca, North American, Pacific, and Southward American plates. A few of the smaller plates are the Anatolian, Arabian, Caribbean, Cocos, Philippine, and Somali plates.

References

Beatty, J. K. and A. Chaikin, eds. The New Solar Arrangement. Massachusetts: Sky Publishing, third Edition, 1990.

Press, Frank and Raymond Siever. World. New York: W. H. Freeman and Company, 1986.

Seeds, Michael A. Horizons. Belmont, California: Wadsworth, 1995.

Globe

Calvin J. Hamilton

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Source: http://www.if.ufrgs.br/ast/solar/earthint.htm#:~:text=Plate%20tectonics%20involves%20the%20formation,topographic%20features%20are%20consequently%20formed.