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The lithosphere


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grade 7 lesson about the solid part of the Earth - Lithosphere

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The lithosphere

  1. 1. Layers of the Earth
  2. 2. 4. The 6-35 km (4-21 miles) thick lithosphere. Earths crust. 3. The 2900 km (1.800 miles) thick Mantle layer formed from rapidly flowing magma. 2. The 2000 km (1,250 miles) thick outer core containing such molten heavy metals as nickel and iron.1. The 1370 km (851 miles) thick inner core, which is in acrystalline state because of the influence of heat andhigh pressure.
  3. 3. Lithosphere The solid part of the earth. It consists of three main layers: crust, mantle and core.
  4. 4. The CrustIs the outermost layer of the earth.Has a depth of about 32 to 40 km.The thinnest layer.The uppermost layer is known as the SIAL. It is composed mainly of silicon and aluminumThe bottom layer of the crust is called SIMA It is made mostly of silicon and magnesium.
  5. 5. Crust are further divided into two major parts: Continental crust It is about 32 kilometers thick, made mainly of granite rocks. The elevated portion of the crust. Oceanic Crust The ocean bed, it is about seven kilometers thick and made mainly of basalt.
  6. 6. The Mantle Located just below the crust. It is denser than crust, about 2,900 km thick. It is composed mainly of very hot, solid rocks that flow. The region between the crust and the mantle is called MOHOROVICIC DISCONTINUITY OR MOHO. Scientists have been able to confirm the differences in density between rocks of the crust and those of the mantle by studying the Moho.
  7. 7. The Core It is about 4,960 km deep. It is divided into: Outer core It is about 2,270 km thick Composed mainly of nickel and iron melted by intense heat. The temperature ranges from 4,000 C to 5,000 C Inner Core It is composed mainly of solid iron and nickel. The temperature is around 5,000 C to 6,000 C. The pressure is exceedingly high.
  8. 8. Materials of the Earth
  9. 9. Igneous Rocks
  10. 10. (1) Basalt: are dark colored, fine-grained extrusive rocks. The mineral grains are so fine that they are impossible to distinguish with the naked eye or even a magnifying glass. They are the most widespread of all the igneous rocks. Most basalts are volcanic in origin and were formed by the rapid cooling and hardening of the lava flows. Some basalts are intrusive having cooled inside the Earths interior.
  11. 11. (2) Gabbro: is a dark-colored, coarse-grained intrusive igneous rock. Gabbro is very similar to basalt in its mineral make up.
  12. 12. (3) Pumice: is a very light colored, frothy volcanic rock. Pumice is formed from lava that is full of gas. The lava is ejected and shot through the air during an eruption. As the lave hurtles through the air it cools and the gases escape leaving the rock full of holes. Pumice is so light that is actually floats on water. Huge pumice blocks have been seen floating on the ocean after large eruptions. Pumice is ground up and used today in soaps, abrasive cleansers, and also in polishes.
  13. 13. (3) Pumice: is a very light colored, frothy volcanic rock. Pumice isformed from lava that is full of gas. The lava is ejected and shotthrough the air during an eruption. As the lave hurtles through theair it cools and the gases escape leaving the rock full of holes.Pumice is so light that is actually floats on water. Huge pumiceblocks have been seen floating on the ocean after large eruptions.Some lava blocks are large enough to carry small animals. Pumiceis ground up and used today in soaps, abrasive cleansers, and alsoin polishes.
  14. 14. (4) Rhyolite: is very closely related to granite. Thedifferences is rhyolite has much finer crystals. Thesecrystals are so mall that they can not be seen by thenaked eye. Rhyolite is an extrusive igneous rock havingcooled much more rapidly than granite, giving it aglassy appearance. The minerals that make up rhyoliteare quartz, feldspar, mice, and hornblende.
  15. 15. (5) Granite: is an igneous rock that is composed of four minerals. These mineralsare quartz, feldspar, mica, and usually hornblende. Granite forms as magmacools far under the Earths surface. Because it hardens deep underground, itcools very slowly. This allows crystals of the four minerals to grow large enoughto be easily by the naked eye. Granite is an excellent material for buildingbridges and buildings because it can withstand thousands of pounds of pressure.It is also used for monuments because it weathers slowly. Engraving in granitecan be read for hundreds of years, making the rock more valuable. Granite isquarried in many places in the World including the United States. The state ofHew Hampshire has the nickname "Granite State" because of the amount ofgranite in the mountains of that beautiful state. The Canadian Shield of NorthAmerican contains huge outcroppings (surface rocks) of granite.
  16. 16. (6) Obsidian: is a very shiny natural volcanic glass. When obsidianbreaks its fractures with a distinct conchoidal fracture. Obsidian isproduced when lava cools very quickly. The lave cools so quicklythat no crystals can form. When people make glass they melt silicarocks like sand and quartz then cool it rapidly by placing it inwater. Obsidian in produced in nature in a similar way. Obsidian isusually black or a very dark green, but it can also be found in analmost clear form. Ancient people throughout the World haveused obsidian for arrowheads, knives, spearheads, and cuttingtools of all kinds. Today obsidian is used as a scalpel by doctors invery sensitive eye operations.
  17. 17. Metamorphic Rock:(1) White Marble: is a metamorphosed limestone or dolomite. both limestoneand dolomite have a large concentration of calcium carbonate (CaCO3). Marblehas many different sizes of crystals. Marble has many color variances due tothe impurities present at formation. Some of the different colors of marble arewhite, red, black, mottled and banded, gray, pink, and green. Marble is muchharder than its parent rock. This allows it to take a polish which makes it a goodmaterial for use as a building material, making sink tops, bathtubs, and acarving stone for artists. Today, headstones are made from marble and granitebecause both of these rocks weather very slowly and carve well with sharpedges. Marble is quarried in Vermont, Tennessee, Missouri, Georgia, andAlabama.
  18. 18. (2) Slate: is a fine-grained metamorphic rock with perfect cleavage that allows itto split into thin sheets. Slate usually has a light to dark brown streak. Slate isproduced by low grade metamorphism, which is caused by relatively lowtemperatures and pressures. Slate has been used by man in a variety of waysover the years. One use for slate was in the making of headstones and gravemarkers. Slate is not very hard and can be engraved easily. The problem with theslate though is its perfect cleavage. The slate headstones would crack and splitalong these cleavage planes. This in not a desirable attribute for a headstone.Slate was also used for chalk boards. The black color was good as a backgroundand the rock cleaned easily with water. Today it is not very advantageous to usethis rock because of its weight and the splitting and cracking over time.
  19. 19. (3) Schist: is a medium grade metamorphic rock. This means thatis has been subjected to more heat and pressure thanslate, which is a low grade metamorphic rock. The individualgrains of minerals can be seen by the naked eye. Many of theoriginal minerals have been altered into flakes. Because it hasbeen squeezed harder than slate it is often found folded andcrumpled. Schists are usually named by the main mineral fromwhich they are formed. Bitotite mica schist, hornblendeschist, garnet mica schist, and talc schist are some examples ofthis.
  20. 20. (4)Gneiss: is a high grade metamorphic rock. This means thatgneiss has been subjected to more heat and pressure than schist.Gneiss is coarser than schist and has distinct banding. Thisbanding has alternating layers that are composed of differentminerals. The minerals that compose gneiss are the same asgranite. Feldspar is the most important mineral that makes upgneiss along with mica and quartz. Gneiss can be formed from asedimentary rock such as sandstone or shale, or it can be formedfrom the metamorphism of the igneous rock granite. Gneiss canbe used by man as paving and building stone.
  21. 21. (5) Quartzite: is composed of sandstone that has beenmetamorphosed. Quartzite is much harder than theparent rock, sandstone. It forms from sandstone thathas come into contact with deeply buried magmas.Quartzite looks familiar to its parent rock. The best wayto tell quartzite from sandstone is to break the rocks.Sandstone will shatter into many individual grains ofsand while quartzite will break across the grains.
  22. 22. (6) Anthracite Coal: is organic sedimentary rocks formed from the build up and decay ofplant and animal material. This usually forms in swamp regions in which there is anabundant supply of growing vegetation and low amounts of oxygen. The vegetation buildsso quickly that new layers of vegetation bury the dead and decaying material very quickly.The bacteria that decay the vegetation need oxygen to survive. Because these decayinglayers are buried so fast the bacteria use up what oxygen there is available and can notfinish the decomposition of the vegetation. The overlaying layers become so heavy thatthey squeeze out the water and other compounds that aid in decay. This compressedvegetation forms coal. The longer and deeper that coal is buried makes it of higherquality. Peat is the first stage of coal formation. Lignite is the next grade of coal followedby bituminous and the highest grade, anthracite. Anthracite is actually a metamorphicrock. It forms during mountain building when compaction and friction are extremely high.This form of coal burns very hot and almost smokeless. It is used in the production of highgrade steel.
  23. 23. Sedimentary Rocks:(1) Limestone: is the most abundant of the non-clastic sedimentary rocks.Limestone is produced from the mineral calcite (calcium carbonate) andsediment. The main source of limestone is the limy ooze formed in the ocean.The calcium carbonate can be precipitated from ocean water or it can beformed from sea creatures that secrete lime such as algae and coral. Chalk isanother type of limestone that is made up of very small single-celledorganisms. Chalk is usually white or gray in color. Limestone can easily bedissolved by acids. If you drop vinegar on limestone it will fizz. Put a limestonerock into a plastic jar and cover it with vinegar. Cover the jar and watch thebubbling of the calcium carbonate and also the disintegration of the rock overa few days.
  24. 24. (2) Breccia: is formed in a very similar fashion toconglomerate. The difference between the two rocks isthat breccias rock fragments are very sharp andangular. These rock fragments have not beentransported by water, wind, or glaciers long enough tobe rounded and smoothed like in the conglomerate.The cementing agents silica, calcite (CaCO3), and ironoxides are the same as in conglomerate.
  25. 25. (3) Conglomerate: is a clastic sedimentary rock that forms fromthe cementing of rounded cobble and pebble sized rockfragments. Conglomerate is formed by river movement or oceanwave action. The cementing agents that fill the spaces to form thesolid rock conglomerate are silica, calcite, or iron oxides. Notice inthe photo above the rounded rock particles in the conglomerate.These rounded particles make conglomerate different frombreccia.
  26. 26. (4) Sandstone: is a clastic sedimentary rock that formsfrom the cementing together of sand sized grainsforming a solid rock. Quartz is the most abundantmineral that forms sandstone. Calcium carbonate, silica,or iron has been added to the water that is in contactwith the sand grains. These minerals grow crystals inthe spaces around the sand grains. As the crystals fillthe gaps the individual sand grains are now transformedinto a solid rock.
  27. 27. (5) Halite: is common table salt. It forms where brakish (salty)lakes or sea beds dry up. This evaporation of the water causes thesalt to precipitate forming the salt crystals. Halite frequentlyoccurs in crystal form. It is usually colorless but can be reddishbrown because of iron oxides in the water that it forms in. Halitehas perfect cleavage and a hardness o 2.5 on the Mohs hardnessscale.
  28. 28. Story 1: "Rock"in StoriesKate was in her career development class atCherokee Middle School. She was very interestedin the subject of earth science and wanted toknow more about Geology and the formation ofrocks through geochemical process, such as,igneous, metamorphic and sedimentary.She interviewed a scientist, Dr. Gutierrez atSouthwest Missouri State University to feed hercuriosity. They planned a journey to theSpringfield rock quarry. Kate met Dr. Gutierrez andthey traveled to the rock quarry.
  29. 29. Kate and Dr. Gutierrez had to wear helmets to enter therock quarry due to the blasting of slabs of stone withdynamite. Kate was overwhelmed with all the differentkinds of rocks. She picked up a light whitish grey rock.Dr. Gutierrez told her the rock was composed ofCalcium Carbonate, CaC03, This type of rock is formedfrom sea creatures that secrete lime, such as algae andcoral. When they die their remains pile up on the oceanfloor and form this rock.What kind of rock would this be? What stage ofthe rock cycle is the rock found? Limestone - Sedimentary
  30. 30. Dr. Gutierrez informed her that the rockshe found is the parent of another kind ofrock that is much harder. This rock is madeup of different sizes of crystals and hasmany variations in color. This rock may bered, white, pink, or grey. It is used as abuilding material to make countertops and bathtubs.What kind of rock would this be? Whatstage of the rock cycle is this rock found? Marble - Metamorphic
  31. 31. The beginning of these rocks occurred 30meters below the Earths surface. There therock was dark colored and fined grained. Thisrock is the most widespread of this stage ofrocks. This rock is volcanic in origin and formedby rapid cooling and hardening of lava.What kind of rock would this be? Whatstage of rock cycle is this rock found? Basalt - Igneous
  32. 32. Story 2Whitney, a very intelligent graduate, completing hermasters in Geology decided to go on a research field classfor the summer. The instructor for this class was Dr.Playmate, a Geologist of Southwest Missouri StateUniversity.They traveled to the Rocky Mountains for their geologicalresearch. While hiking, they discovered an exposed cliffthat had been subjected to weathering.Within this cliff they found a rock that was composed ofthe minerals feldspar, mica, and quartz. This rock had abanned appearance in its layers.What kind of rock would this be? What stage of rockcycle is this rock found? Gneiss - Metamorphic
  33. 33. Whitney informed her classmates that thisrock can be formed from several other typesof rocks. One of these rocks forms from thecementing together of small grains. Quartz isthe most abundant mineral in this kind of rock.What kind of rock would this be? What stage ofrock cycle is this rock found? Sandstone - Sedimentary
  34. 34. The rock in the cliff could also be formed from acompletely different type of rock. This rock is composedof four minerals: quartz, feldspar, mica, andhornblende. This rock forms as magma cools far underthe Earths surface. Because it hardens underground, itcools slowly. This allows the crystal of the four mineralsto grow large enough to be seen by the naked eye. Thistype of rock is excellent of building bridges andmonuments because it weathers slowly.What kind of rock would this be? What stage ofrock cycle is this rock found? Granite - Igneous
  35. 35. Story 3:Jessica, after completing a very rough semesterat Southwest Missouri State University, decidedto take a vacation to Hawaii with her frequentflyer miles. She decided to go to the NationalVolcano Park to elevate some stress. The parkencompasses diverse environments that rangefrom seal level to the summit of the Earthsmost massive volcano, Mauna Loa at 13,677feet. After a recent volcanic eruption she took aguided tour. On this tour, she observed manydifferent types of volcanic rock.
  36. 36. One in particular was very light colored and lightin weight. This rock is so light that it floats onwater. It had holes all throughout the rock. Thisrock is formed when lava is ejected and shotthru the air during a volcanic eruption. As thelava flies thru the air it cools and gases escapeleaving the rock full of holes. This rock is usedtoday in soap and abrasive cleaners.What kind of rock would this be? What stage ofrock cycle is this rock found? Pumice - Igneous
  37. 37. They traveled on and came to a beautiful flowingstream. The guide picked up a hand full of rocksand Jessica noticed one that appeared to havemany tiny rocks inside of it. This rock wasformed by river movement and composed ofrounded cobble and pebble sized rock fragments.What kind of rock would this be? Whatstage of rock cycle is this rock found? Conglomerate - Sedimentary
  38. 38. After the guided tour, Jessica to take a walk onthe beach of Hawaii. As she walked, she pickedup shells and rocks from the sand. She noticedone of the rocks looked like it had been formedfrom the cementing together of small sand sizedgrains. This rock looked like sandstone, butwhen broken, the grains of sand broke into layers.What kind of rock would this be? Whatstage of rock cycle is this rock found? Quartzite - Metamorphic
  39. 39. Rock Name Description Rock Type Dark colored, fine grained; formed by rapid Basalt Igneous cooling and hardening of lava flow Dark colored, coarse-grained; similar to basalt Gabbro but mostly composed of the mineral Igneous plagioclase feldspar Light colored, frothy volcanic rock; formed Pumice when lava is ejected and shot through the air Igneous during an eruption; so light is can float Closely related to granite, but has very fine Rhyolite crystals; has a glassy appearance; made up of Igneous quartz, feldspar, mica and hornblende Composed of the same minerals as rhyolite; Granite forms as magma cools far under the earths Igneous surface Very shiny natural volcanic glass; produced Obsidian when lava cools very quickly so no crystals Igneous form; usually black or very dark green;
  40. 40. MineralsThey are naturally formed solid elementsor compounds having a crystallinestructure and possessing physical andchemical properties.They are considered as the building unitsof the Lithosphere.
  41. 41. The element composing the MineralsOxygen Oxygen in its combined form is the most abundant element composing minerals. It is found chemically combined with other elements forming OXIDES. Very few minerals are found to be composed of pure elements.
  42. 42. What is the relationship of Rocks and Minerals?Are familiar with a fruit cake? Fruit cake is a loaf of bread with nuts, raisins and glazed fruits. The fruit cake represents the rock, the nuts, raisins and glazed fruits represents the
  43. 43. Properties used in Identifying MineralsMINERALOGY is the science that dealswith the identification and classification ofminerals.Mineralogists subject the minerals tovarious tests to determine their properties.
  44. 44. Properties used in Identifying Minerals 1. Color This is the most obvious property of mineral. However, not all minerals can be identified by color for three reasons: a) Many minerals are colorless or else they have the same color. b) Impurities affect the real color of the mineral. c) Surface color tarnishesExample: Corundum is a colorless mineral. With traces ofChromium, it becomes red called (ruby) and with traces ofiron and titanium it becomes blue called ( sapphire)
  45. 45. 2. Luster This is the property of the mineral to reflect, refract or absorb light. Some minerals “shine’ when exposed to light while others do not. Some terms used to describe luster are: BRILLIANT, DULL, PEARLY, SILKY, EA RTHY and many more.
  46. 46. 3. Streak The color of the fine powder of the mineral made against a streak plate. Some minerals have streaks similar to their color. Others have streaks different from their colors. Gold is yellow, and its streak is also yellow. Pyrite (known as fool’s gold) has a greenish-black streak. Hematite is black but its streak is red.
  47. 47. Identifying Mineralsby StreakGold(top), platinum(middle) andcopper (bottom)have characteristicstreak colors, bestseen on a blackstreak plate.
  48. 48. 4. Crystal Form Minerals are usually crystalline and some minerals have enchanting crystals. Crystal form reveals the arrangement of atoms in a mineral. The atoms of each mineral are arranged in a definite geometric pattern. Each mineral had its own definite atomic arrangement which is helpful in identifying that particular mineral.
  49. 49. 5) Cleavage and Fracture This property reveal the structure of a mineral. Cleavage is the splitting of the mineral readily along certain planes to produce flat and smooth surfaces. Uneven breaks or cracks that form uneven surfaces are called FRACTURE.
  50. 50. 6. Specific Gravity This is the number that tells how many times denser the minerals is than an equal volume of water. In determining the specific gravity of a mineral. Its volume and mass are first determined. Then the density is computed using the formula: D=M/V
  51. 51. The resulting density is compared with the density ofwater which is equal to 1 g/cm3.For example, the density of silver is 10.6 g/cc. This isthen compared to the density of water. Thus,Specific gravity = density of silver / density of water = 10.6 g/cc / 1g/cc = 10.6Silver is 10.6 times denser than water.
  52. 52. Specific Gravity of Some Minerals Minerals Specific Gravity Gold 19.3 Mercury 13.6 Platinum 21.5 Silver 10.6 Copper 9.0 Zinc 7.1 Pyrite 5.2 Garnet 4.2 Diamond 3.5 Talc 2.8 Calcite 2.7 Quartz 2.6
  53. 53. 7. Hardness This is the resistance of a mineral to being scratched. The test for the hardness of a mineral involves the use of scale invented by Friedrich Mohs.
  54. 54. The Moh’s Scale of Hardness1. Talc 6. Orthoclase2. Gypsum 7. Quartz3. Calcite 8. Topaz4. Fluorite 9. Corundum5. Apatite 10. Diamond
  55. 55. The Forces the Construct theEarth’s Surface
  56. 56. Diastrophism or Crustal WarpingPertains to all the movements of the solidparts of the earth.Great forces act on the crust causing it tomove.Sometimes: the movement is so strong and sudden that we can feel the shaking of the ground. the movement may be so slow that we can not feel them, can only be detected by a seismograph.The great forces that cause the felt and unfeltmovements of the crust have been identified aspushes (compression) and pulls (tension) exerted onthe crust over long period of time.
  57. 57. Direction of Forces and the Movement they Produce1. Upward forces Upward forces cause the local widespread rising or uplift of the crust. These forces are responsible for the emergence of small islands in the deep seas of the pacific. The discovery of the fossil remains of marine organisms in the rock layers of high areas indicates that these layers were pushed up from under the water of the ocean.
  58. 58. 2. Downward Forces Downward forces cause the local or widespread sinking or subsidence of the crust. These forces caused the disappearance of small islands in the pacific in the historic past. The fossil remains found in the rock layers reveal that there was at one time a land bridge connecting Asia and North Africa. Such a land bridge and many more have been submerge or pushed underwater by great forces.
  59. 59. 3. Sideward Forces Sideward forces cause the horizontal motion of the crust called thrust. Large masses of rocks slide and slip against each other into new position. Sometimes rock masses bend, tilt, or wrinkle due to these sideward forces.
  60. 60. Effects of DiastrophismThe movement of the crust broughtabout by the interaction of theforces described has resulted in theformation of the different surfacefeatures of the earth.
  61. 61. 1. FoldingFolding occurs when the crust crumples orwrinkles due to compressions or pushesfrom opposite directions.
  62. 62. As the crust is crumpled, the rock stratabecome tilted.
  63. 63. The materials of the crust are dense andrigid, but under great heat and pressure,they soften and can be deformed.The crest or upward curve of a fold iscalled anticline.The trough or downward curve is calledsyncline.
  64. 64. The crest may formmountains, hills or ridges and thetrough may form valley.
  65. 65. 2. FaultingFaulting occurs when a rock massesof the crust are pulled apart (tension)forming cracks or fractures on thecrust.The tensional forces go beyond theelastic limit of the crust that it yieldsto the stress by breaking.
  66. 66. Different Tensional Stress and its Effects
  67. 67. In some instances, parallel faults mayoccur in the crust. The area between two parallel faults may eventually sink as the downward forces act on it.The sunken area is called a graben and itmay form rift valley.The risen area is called ahorst and it may becomea plateau.
  68. 68. Types of Faulting
  69. 69. We can now conclude that throughgreat stretches of time, ocean floorshave been lifted up, high areas havebeen thruster, pushed down, pushedand pulled sideways many times.Careful observations indicate thatthese processes are still going on andaffecting the crust.Where do the forces that shapethe earth come from?
  70. 70. Causes of Diastrophism1. Continental Drift TheoryThis theory wasproposed by AlfredWegener, a Germanscientist in 1915.
  71. 71. According to him, 200 million yearsago, there was only a singlesupercontinent called Pangaea situated atthe center near the equator.
  72. 72. This single supercontinent broke up into pieces which drifted slowly away from each other. The pieces formed the continents of today.As the continents driftedapart, they rubbed and collidedagainst each other forming thesurface features of today.
  73. 73. Assignment: 1. Make at least 300 words reaction paper on the video presentation. 2. Long bond paper. 3. Hand written. 4. Follow the web site below
  74. 74. 2. The Theory of Seafloor SpreadingIn 1920, five years after Wegener’s theory wasformulated, the existence of the mid-oceanic ridges werediscovered using an echo-sounding device like a sonar.
  75. 75. A break or rift was found at the middle of the ridgerunning along its length where basaltic magma wells out tothe surface.
  76. 76. This basaltic magma solidified forming a “new crust”.
  77. 77. The new crust pushes the old crust causing the ocean floor tospread.
  78. 78. The force according to theory caused thebreaking and drifting apart of the continents.The mid-oceanic ridges are believed to be theremnants of the continents that drifted.The ocean floor has been estimated to bespreading at the rate of 5 cm per year.This rate may seem slow, but for the past 200million years, all the existing ocean basin weregenerated through this slow movement.
  79. 79. An exploration using a research shipnamed Glomar Challenger drilled throughthe crust and gathered several rocksamples from both sides of the mid-oceanic ridge.
  80. 80. Radioactive dating techniqueproved that the rocks found fromabout the same distance from therift on both sides are of the sameage and rock type.The rocks taken near the ridgewere relatively younger thanthose further from the ridge.
  81. 81. If new crust is continuously beingformed, does it mean that the earth’sdiameter is expanding?Scientists explain that as a new crustis formed at the mid-oceanicridges, elsewhere on earth, the oldcrust is being destroyed at the samerate that it is created.The region where the old crust isbeing destroyed is called thesubduction zone.
  82. 82. Here in the subduction zone, the old crust is plungedinto high pressure and high temperatureenvironment.Thus, some of the materials melt and may migrateupward giving rise to volcanic eruptions.
  83. 83.
  84. 84. 3. The Plate Tectonic TheoryThis theory proposed that theLithosphere is divided into six majorplates.
  85. 85. The plate may be composed of thecontinental crust on top of the oceaniccrust or may be composed of the oceaniccrust alone.
  86. 86. The plates are slowly, but nevertheless continually in motion. The movement of plates is believed to be caused by the convection currents in the mantle.As the magma from the lower mantle rises fromdeep within the earth and spreads laterally, theplates are set in motion.Thus, the movement of the plates generatesearthquakes, volcanic activities, as well as pushesand pulls causing the deformation of large masses ofrocks.
  87. 87. Thus, the movement ofthe plates generatesearthquakes, volcanicactivities, as well aspushes and pullscausing the deformationof large masses of rocks.
  88. 88. As the movement of the plates goeson, interaction occurs along their plateboundaries.Plate boundary is the place where two platesmeet.
  89. 89. The plate boundaries1. Spreading or divergent boundary An area where two plates move apart leaves a gap between them. The gap formed is immediately filled up with molten materials that wells up from the lower mantle.
  90. 90. The Atlantic ocean, the Great Rift Valley of Africa andthe Red Sea are believed to be formed by this type ofmovement of the plates.
  91. 91. 2. Colliding or convergent boundaryThis is an area where two platesmove toward each other. As the plates collide, the leading edges of one plate is bent downward allowing it to slide beneath the other. As all cases, the denser materials plunge beneath the surface.
  92. 92. The colliding boundary is the site where the old crust isbeing destroyed (subduction zone).The Himalayan Mountain Ranges, Andes Mountain,and the Marianas Trench are believed to be formed bythis type of plate movement.
  93. 93. Andes Mountain
  94. 94. 3. Fracture or transform boundaryThis is the area where two plates move past eachother, sliding, scraping and deforming the edges ofcontinents.
  95. 95. The San Andreas Fault of California is a famous example. The Pacific plate is moving towards northeast past the North American plate. Los Angeles is located on a plate situated on one side of the fault. San Francisco is located on another plate. In about 10 t0 15 million years, Los Angeles and San Francisco will be located next to each other.