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- 1. Structure of the Earth and Plate Tectonics
- 2. Objectives At the end of the lesson, the students should be able to: 1. Explore the Earth's internal structure, including its layers. 2. Understand the principles of plate tectonics and how they shape the Earth's surface. 3. Examine the theory of diastrophism and its effects on the Earth's surface 4. Investigate the theory of continental drift and the evidence supporting the movement of tectonic plates. 5. Analyze the process of seafloor spreading and its role in forming and shifting tectonic plates.
- 4. The structure of the earth is divided into four major components: the crust, the mantle, the outer core, and the inner core. Each layer has a unique chemical composition, physical state, and can impact life on Earth's surface.
- 5. The Earths Crust -is the outermost layer and the one we interact with directly. It varies in thickness, with oceanic crust being thinner (about 4-7 miles or 6-11 kilometers) and continental crust being thicker (averaging about 19 miles or 30 kilometers).
- 6. The Earths crust is where we find the Earths landforms, such as mountains, valleys, and plains, as well as the ocean floor. The crust is primarily composed of solid rock, with different types of rock prevailing in continental and oceanic regions. Continental crust is mostly made up of granitic rocks, while oceanic crust is primarily composed of basaltic rocks.
- 7. The Earths Mantle The mantle is located beneath the Earths crust and extends to a depth of about 1,800 miles (2,900 kilometers). It is the thickest layer of the Earth. The heat generated from the Earths interior and the decay of radioactive elements contribute to the high temperatures within the mantle.
- 8. The mantle is composed of solid rock, primarily silicate minerals. Although it is solid, the mantle behaves like a very viscous or plastic material over geological timescales. This property allows the mantle to flow slowly, leading to the movement of tectonic plates and the associated geological phenomena like earthquakes and volcanoes.
- 9. The Earths Core The Earths core is divided into two parts: the outer core and the inner core.
- 10. Outer Core The outer core is located beneath the mantle, beginning at a depth of about 1,800 miles (2,900 kilometers) and extending to around 3,500 kilometers below the surface. It is primarily composed of molten iron and nickel. The high temperatures and pressures in the outer core keep these materials in a liquid state. The motion of molten iron in the outer core is responsible for generating the Earths magnetic field through the geodynamo process.
- 11. Inner Core The inner cores solid nature is important for understanding the Earths internal dynamics, including how seismic waves pass through it. The inner core is situated at the very center of the Earth, starting at a depth of about 3,500 kilometers. It is primarily composed of solid iron and nickel. Despite the extremely high temperatures at this depth, the inner core remains solid due to the tremendous pressure.
- 13. Diastrophism The diastrophism word comes from the Greek word diastrophe which means distortion or dislocation It refers to the deformation of the Earth's crust due to tectonic forces. It encompasses various processes that result in the folding, faulting, and uplifting of the Earth's crust.
- 16. WHAT IS PLATE TECTONIC The theory of plate tectonics explains diastrophism as the result of the movement and interaction of Earth's lithospheric plates. A scientific theory that explains how major landforms are created as a result of Earth's subterranean movements.
- 17. Plate motions cause mountains to rise where plates push together, or converge, and continents to fracture and oceans to form where plates pull apart, or diverge. The continents are embedded in the plates and drift passively with them, which over millions of years results in significant changes in Earth's geography.
- 18. Movement of Plates The slow movement of hot, softened mantle lies below rigid plates. The hot, softened rock in the mantle moves in a circular manner in a convection flow the heated, molten rock rises to the surface, spreads, and begins to cool, and then sinks back down to be reheated and rises again.
- 19. Different Types of Plate Boundaries
- 20. 1. Divergent Plate Boundaries Divergent Boundary - also called as constructive boundary, formed when two tectonic plates move apart from each other creating tension. Along these boundaries, earthquakes are common and magma (molten rock) rises from the Earths mantle to the surface, solidifying to create new oceanic crust.
- 22. The Mid-Atlantic Ridge is an example of divergent plate boundaries.
- 23. 2. Convergent Plate Boundaries This occurs when plates move towards each other and collide. When a continental plate meets an oceanic plate, the thinner, denser, and more flexible oceanic plate sinks beneath the thicker, more rigid continental plate. This is called subduction.
- 24. 3 Types of Convergent Boundaries
- 25. a. Oceanic-Continental Boundaries When oceanic and continental plates collide, the oceanic plate undergoes subduction and volcanic arcs arise on land. These volcanoes release lava with chemical traces of the continental crust they rise through. Oceanic plates are denser than continental plates, which means they have a higher subduction potential. Examples of ocean-continent convergent boundaries are: 1.Subduction of the Nazca Plate under South America which has created the Andes Mountains and the Peru Trench 2. Subduction of the Juan de Fuca Plate under North America created the Cascade Range
- 26. In Oceanic-Continental plate boundary and two oceanic plates boundary, the oceanic plate bends downward into the mantle through the process called subduction. A subduction is a collision between two of Earth's tectonic plates, where one plate sinks into the mantle underneath the other plate.
- 27. b. Oceanic-Oceanic Boundaries When two oceanic plates collide, the denser plate sinks below the lighter plate and eventually forms dark, heavy, basaltic volcanic islands. When oceanic plates are subducted, they often bend, resulting in the formation of oceanic trenches. These often run parallel to volcanic arcs and extend deep beneath the surrounding terrain. The deepest oceanic trench, the Mariana Trench, is more than 35,000 feet below sea level. It is the result of the Pacific Plate moving beneath the Mariana Plate.
- 28. c. Continental-Continental Boundaries Continental-continental convergent boundaries pit large slabs of crust against each other. This results in very little subduction, as most of the rock is too light to be carried very far down into the dense mantle. Instead, the continental crust at these convergent boundaries gets folded, faulted, and thickened, forming great mountain chains of uplifted rock. The Himalayas and the Tibetan Plateau, the result of 50 million years of collision between the Indian and Eurasian plates, are the most spectacular manifestation of this type of boundary.
- 29. 3. Transform Plate Boundaries is formed when two plates are sliding past each other. It is also called the Strike-slip fault. Rocks that line the boundary split into pieces as the plates slip at each other. A crack is then formed creating an undersea canyon or linear fault valley. San Andreas Fault is an example
- 31. What features form at plate tectonic boundaries?
- 32. Fold mountains are created where two or more of Earth's tectonic plates are pushed together. At these colliding, compressing boundaries, rocks and debris are warped and folded into rocky outcrops, hills, mountains, and entire mountain ranges. Fold mountains are created through a process called orogeny. Formation of Folds
- 33. Formation of Faults It forms when rock above an inclined fracture plane moves downward, sliding along the rock on the other side of the fracture. Normal faults are often found along divergent plate boundaries, such as under the ocean where new crust is forming. Long, deep valleys can also be the result of normal faulting.
- 34. Formation of Trenches Trenches are formed by subduction, a geophysical process in which two or more of Earth's tectonic plates converge and the older, denser plate is pushed beneath the lighter plate and deep into the mantle, causing the seafloor and outermost crust (the lithosphere) to bend and form a steep, V-shaped depression.
- 35. Formation of Volcanoes Magma rises from the hot spots and erupts as lava through cracks in the Earth's surface forming volcanoes. As a plate moves slowly across a hot spot, a chain of volcanoes or volcanic islands can form. The islands of Hawaii and Samoa were formed in this way.
- 36. Formation of Rift Valley A rift valley is a lowland region that forms where Earth's tectonic plates move apart, or rift. Rift valleys are found on land and at the bottom of the ocean, where they are created by the process of seafloor spreading.
- 37. Formation of Mountain Range Mountains form where two continental plates collide. Since both plates have a similar thickness and weight, neither one will sink under the other. Instead, they crumple and fold until the rocks are forced up to form a mountain range. As the plates continue to collide, mountains will get taller and taller.
- 39. Continental Drift The theory of continental drift, proposed by Alfred Wegener in the early 20th century, suggests that the Earth's continents were once joined together in a single supercontinent called Pangaea. Over time, the continents drifted apart due to the movement of tectonic plates. Wagner believed in three-layer system; outer layer of sial, intermediate layer of sima and lower layer of nife. (sial is restricted to continent only and sialic masses float over)
- 40. According to Wegener, all continents formed a single continental mass (PANGEA) & mega ocean (PANTHALASSA) surrounded the same.
- 41. Around 200 million years ago, Pangaea first broke into two large continental masses as Laurasia (Present day- N. America, Europe and Asia) and Gondwana (Present day S. America, Africa, India, Australia and Antarctica). Subsequently, Laurasia and Gondwanaland continued to break into various smaller continents that exist today.
- 43. The continents fit together like pieces of a puzzle. This is how they looked 250 million years ago. Alfred Wegener proposed that the continents were once united into a single supercontinent named Pangaea, Topographic Evidence meaning all earth in ancient Greek. He suggested that Pangaea broke up long ago and that the continents then moved to their current positions.
- 44. Movement of the Plates Over Time
- 45. One type of evidence that strongly supported the Theory of Continental Drift is the fossil record. Scientists have found fossils of similar types of plants and animals in rocks of similar age. These rocks were on the shores of different continents. This suggests that the continents were once joined. For example, fossils of Mesosaurus, a freshwater reptile, have been found both in Brazil and western Africa. Also, fossils of the land reptile Lystrosaurus have been found in Africa, India and Antarctica. Fossil Evidence
- 46. Scientists have found that rocks on the east coast of South America are the same as rocks found on the west coast of Africa. These rocks are different from rocks found in other places on Earth, suggesting that the continents were once connected. Plant and animal fossils also reveal evidence. Rock Formation Evidence
- 50. Convection Currents This theory suggests that diastrophism is driven by convection currents in the Earth's mantle. Heat from the Earth's core causes the mantle material to heat up and rise, while the cooler material sinks. Mantle convection describes the movement of the mantle as it transfers heat from the white-hot core to the brittle lithosphere. The mantle is heated from below, cooled from above, and its overall temperature decreases over long periods of time. All these elements contribute to mantle convection.
- 52. What are the effects of convection in the mantle? The mantle's convective motions break the lithosphere into plates and move them around the surface of the planet. These plates may move away from, move by, or collide with each other. This process forms ocean basins, shifts continents, and pushes up mountains.
- 54. Seafloor spreading Seafloor spreading is a geologic process in which tectonic plateslarge slabs of Earth's lithospheresplit apart from each other. Seafloor spreading and other tectonic activity processes are the result of mantle convection.
- 56. New geographic features can be created through seafloor spreading. The Red Sea, for example, was created as the African plate and the Arabian plate tore away from each other. Today, only the Sinai Peninsula connects the Middle East (Asia) with North Africa.
- 58. The Theory of Isostasy The Theory of Isostasy by Airy is a fundamental concept in the field of geophysics that seeks to explain the equilibrium and balance of Earth's crust. This theory, proposed by the renowned British mathematician and scientist Sir George Biddell Airy in the 19th century, revolutionized our understanding of how the Earth's lithosphere behaves and its implications for the formation of mountains, continents, and ocean basins. In this article, we will delve into the theory of isostasy, its key principles, and its significance in the field of geography
- 61. References Understanding Plate Motions. USGS. http://pubs.usgs.gov/publications/text/unde rstanding.html Plate Movement. OptIPuter Outreach. http://education.sdsc.edu/optiputer/teacher s/platemovement.html Plate Tectonics. The Way the Earth Works. LHS GEMS, 2002.