Science

• Layers of the Earth

  • Crust
  • Mantle
  • Core
• Crust


  Outermost layer of the Earth, divided into continental crust (thicker, less dense, primarily composed of granite) and oceanic crust (thinner, denser, primarily composed of basalt)
• Mantle


  Lies beneath the crust, thickest layer of the Earth, consists of solid rock that can flow slowly, composition is mainly silicate minerals, upper mantle is more rigid and lower mantle exhibits greater flow
• Core


  Innermost layer of the Earth, composed primarily of iron and nickel, divided into outer core (liquid) and inner core (solid), generates the Earth's magnetic field through the movement of molten iron in the outer core
• Granite


  Igneous rock that forms from the slow cooling and crystallization of magma deep within the Earth's crust
• Basalt


  Igneous rock that forms from the rapid cooling of lava at or near the Earth's surface
• Basalt


  Generally denser and heavier than granite due to its higher iron and magnesium content
• Mafic rocks


  Characterized by their dark color and rich magnesium and iron content, contain minerals like olivine and pyroxene, have lower silica content, resulting in higher density and lower viscosity, commonly found in oceanic crust, basaltic lava flows, and volcanic islands
• Felsic rocks


  Exhibit lighter colors due to their high silica and aluminum content, have lower density and higher viscosity, resulting in more explosive volcanic eruptions, commonly found in continental crust, granite plutons, and volcanic arcs associated with convergent plate boundaries
• Types of plate boundaries

  • Convergent
  • Divergent
  • Transform
• Convergent boundaries


  Where two tectonic plates move towards each other and collide
• Divergent boundaries


  Where two tectonic plates move away from each other
• Transform boundaries


  Where two tectonic plates slide past each other horizontally in opposite directions, crust is neither created nor destroyed, marked by prominent fault lines
• Magma generation at subduction zones

  Oceanic plate subducted beneath continental or oceanic plate, descends into mantle, encounters increasing temperature and pressure, hydrated minerals release water, lowers melting point of surrounding mantle rocks, magma rises through overlying mantle and erupts at the surface, forming volcanic arcs
• Magma generation at continental collision zones

  Intense pressure and heat cause partial melting of lower crust and mantle beneath convergent boundary, generates magma that can ascend through the crust to form volcanic activity
• Volcanism is generally less common in continental collision zones compared to subduction zones
• Earthquakes at subduction zones


  As descending plate bends and breaks, stress is released, causing earthquakes
• Earthquakes at divergent boundaries

  Tensional forces cause the crust to fracture and fault, releasing stored energy in the form of earthquakes
• Earthquakes at transform boundaries

  Frictional resistance builds up along the boundary, when overcome, stored energy is released in the form of earthquakes
• Continental-continental collision


  Neither plate is typically subducted, crust crumples and thickens, leading to the formation of extensive mountain ranges and earthquakes
• Oceanic-oceanic collision

  One plate is usually subducted beneath the other, forming deep ocean trenches, volcanic island arcs, and sometimes chains of volcanic islands
• Oceanic-continental collision


  Denser oceanic plate is subducted beneath the less dense continental plate, leading to the formation of deep ocean trenches, volcanic arcs, and mountain ranges
• Continental rifting


  Divergent boundaries can lead to the formation of rift valleys as the continent splits apart, if rifting continues, it may eventually result in the formation of new ocean basins
• Oceanic rifting


  Divergent boundaries create mid-ocean ridges, where new oceanic crust is formed as magma rises from the mantle and solidifies, leading to the spreading of the seafloor
• Oceanic crust


  Primarily composed of basalt, a dense, dark volcanic rock rich in iron and magnesium, thinner and denser than continental crust
• Continental crust


  Primarily composed of granitic rocks, thicker and less dense than oceanic crust
• Oceanic crust is relatively young because new oceanic crust forms continuously at mid-ocean ridges through volcanic activity, continental crust is much older because it is recycled through processes such as erosion, sedimentation, and tectonic activity, but it is not continuously created like oceanic crust
• Formation of oceans


  Oceans are formed at divergent boundaries through the process of seafloor spreading, where tectonic plates move apart, magma from the mantle rises to fill the gap, solidifying upon reaching the surface to form new oceanic crust, as new crust is continuously added, the ocean basin widens and the newly formed oceanic crust moves away from the ridge axis
• Mantle convection


  Driven by heat transfer within the Earth's mantle, heat from the core causes material in the mantle to become less dense and rise, while cooler, denser material sinks, creating circular motion or convection currents, warm material rising beneath divergent boundaries pushes plates apart, contributing to seafloor spreading and the formation of mid-ocean ridges, cooler material sinking at subduction zones pulls plates downward, initiating the process of subduction
• Ridge push


  Gravitational force resulting from the elevated position and gravitational potential energy of mid-ocean ridges, as new oceanic crust forms at divergent boundaries and pushes plates apart, the elevated ridge creates a slope or gradient that exerts a downward force on the plates away from the ridge axis
• Slab pull


  Gravitational force resulting from the sinking of dense oceanic lithosphere into the mantle at subduction zones, the sinking oceanic plate creates a negative buoyancy force, exerting a pulling force on the rest of the plate
• The Earth's crust maintains its volume over time despite subduction because new crust is continuously formed at divergent boundaries through seafloor spreading, as oceanic plates move apart, magma rises from the mantle to create new crust, offsetting the loss of crust where subduction occurs, additionally, the recycling of crustal material through subduction and volcanic activity helps balance the removal of crust by adding material back into the mantle
• Earth's magnetic field


  Essential for navigation and protecting the planet from harmful solar radiation, generated by the geodynamo theory: as molten iron in the outer core convects due to heat from the core and the Earth's rotation, electric currents are induced, producing the magnetic field, while plate tectonics doesn't directly generate the magnetic field, it influences the distribution of magnetic anomalies on the Earth's surface
• Continental drift


  Hypothesis proposed by Alfred Wegener in the early 20th century, suggesting that continents were once connected as a single supercontinent called Pangaea and have since drifted apart over geological time scales
• Seafloor spreading


  Process proposed by Harry Hess in the 1960s to explain the formation of new oceanic crust at mid-ocean ridges and the widening of ocean basins, molten material (magma) rises from the mantle at mid-ocean ridges, creating new oceanic crust as tectonic plates move apart
• Breakup of Pangaea


  Pangaea, the supercontinent that existed approximately 335 million years ago, began to break apart due to tectonic forces, leading to the formation of two major landmasses: Laurasia in the north and Gondwanaland in the south, over millions of years, the fragments of Gondwanaland continued to drift apart, driven by plate tectonic movements, resulting in the formation of the continents as we know them today
• Seafloor spreading


  The addition of new oceanic crust at mid-ocean ridges leads to the widening of ocean basins, as tectonic plates move apart, they create space for the accumulation of new crust, resulting in the expansion of the ocean floor
• Evidence for plate tectonics

  • Coastline fit of continents
  • Fossil distribution
  • Geological evidence
  • Paleoclimatic evidence
• Alfred Wegener's theory of continental drift faced rejection primarily due to the lack of mechanism to explain how continents could move across the Earth's surface and the circumstantial nature of the evidence presented
• Importance of plate tectonics and Earth's mechanism


  Provides a deep understanding of Earth's geological history, unraveling mysteries surrounding the movement of continents and the evolution of oceans, forms the cornerstone of the plate tectonics theory, which explains natural hazards like earthquakes, volcanic eruptions, and tsunamis, and is invaluable for resource exploration and understanding the interconnectedness of Earth's geological and environmental systems