Plate Tectonics and Earth's Interior

Overview of Plate Tectonics and Earth’s Structure

  • The globe is described by James Hutton as not only a machine but an organized body with regenerative power.

Earth Composition

  • Earth Structure:

    • Geosphere: Composed of rocks and minerals.

    • Hydrosphere: Contains both fresh and saline water.

    • Atmosphere: The layer of gases surrounding Earth.

    • Biosphere: The region of Earth where life exists.

Rocks and Minerals

  • Definitions:

    • Rocks: Aggregates of minerals.

    • Minerals: Naturally occurring crystalline solids with a unique chemical composition, generally inorganic.

  • Components of Granite:

    • Feldspar + Quartz + Hornblende.

  • Building Blocks of the Geosphere: Both rocks and minerals are essential.

Rock Cycle

  • Magma Formation:

    • Occurs when rocks melt deep within the Earth’s surface.

  • Types of Rocks:

    • Igneous Rock: Formed from the cooling and solidification of magma or lava.

    • Formation:

      • Intrusive Igneous Rock: Crystallizes below surface.

      • Extrusive Igneous Rock: Cools on surface.

    • Sedimentary Rock: Formed through compaction and cementation of sediments.

    • Metamorphic Rock: Created from pre-existing rock through heat and pressure (metamorphism).

Earth's Layers

  • Chemical Composition:

    • Crust: 7-70 km thick, composed mainly of silicon, aluminum, and oxygen.

    • Mantle: 2900 km, composed mainly of iron and magnesium.

    • Core: Composed of iron and nickel (inner core solid, outer core liquid).

  • Abundance of Elements in Crust:

    • Most abundant: Oxygen (46.6%), Silicon (27.7%), Aluminum (8.1%), Iron (5.0%), with others like Magnesium (2.1%), Calcium (3.6%), Sodium (2.8%).

Mineral Properties

  • Distinctive Properties:

    • Crystal Form: Outward expression of internal atomic arrangement.

    • Hardness: Measured by Mohs Scale (1-10).

    • Talc (1), Gypsum (2), Calcite (3), Quartz (7), Diamond (10).

    • Cleavage and Fracture: Cleavage refers to breakage along planes of weakness while fracture occurs when bonds break uniformly.

    • Color, Streak, and Luster:

    • Color: Identifiable appearance of the mineral.

    • Streak: Color of mineral when powdered.

    • Luster: How mineral reflects light.

Rock-Forming Minerals

  • Classification:

    • Two groups: Silicates (most abundant, containing silicon-oxygen tetrahedra) and Non-silicates (e.g., carbonates, oxides).

    • Silicates vs Non-silicates:

    • Ferromagnesian (contains iron and magnesium) vs Nonferromagnesian.

    • Major Groups:

    • Carbonates (e.g., Calcite), Sulfates (e.g., Gypsum), Oxides (e.g., Magnetite), Phosphates (e.g., Apatite), and Halides (e.g., Halite).

Formation of Minerals

  • Crystallization: Process of forming solid from liquid or gas.

  • Sources of Crystallization:

    • From Magma (high temp, Bowen's reaction series).

    • From Water Solutions (precipitation of dissolved chemicals).

Types of Rocks Within the Rock Cycle

  • Igneous Rocks: Derived from cooled magma; classifications include:

    • Ultramafic, Basaltic, Andesitic, and Granitic based on silica content.

  • Sedimentary Rocks: Formed from weathering, erosion, deposition, and lithification of pre-existing rocks or chemical processes.

    • Classified as Clastic, Chemical, or Organic.

  • Metamorphic Rocks: Form from pre-existing rocks subjected to metamorphism through added heat/pressure or chemically altered.

    • Classified as Foliated (layered) or Non-foliated (not layered).

Plate Tectonics

  • Theory of Plate Tectonics: Explains motion and interaction of tectonic plates, resulting in geological features.

  • Types of Plate Boundaries:

    • Divergent (plates pulling apart), Convergent (plates pushing together), Transform (plates sliding past).

  • Continental Drift Evidence:

    • Jigsaw fit of continents, fossil distribution, geological similarities, paleoclimatic evidence.

Seafloor Spreading and Paleomagnetism

  • Seafloor Spreading: Oceanic ridges serve as sites for new lithosphere formation and trenches for destruction.

  • Paleomagnetic Evidence: Direction of magnetism in sea floor crust provides information on continental drift and age of rocks.

Atmosphere and Weather

  • Atmospheric Composition: Majority nitrogen (78%), followed by oxygen (21%). negligible variable gases (e.g., CO₂, H₂O).

  • Factors Influencing Weather:

    • Solar energy, uneven heating of Earth, evaporation, and land-water arrangement.

  • Driving Forces of Air Motion:

    • Pressure gradient force due to uneven heating generating wind; influenced by the Coriolis Effect and friction.

Clouds and Precipitation

  • Cloud Development:

    • Atmospheric lifting mechanisms include convection, orographic lifting, and frontal lifting.

  • Types of Clouds: High (Cirrus), Middle (Altostratus), Low (Stratus), and vertically developed clouds (Cumulonimbus).

  • Precipitation: Forms through the collision-coalescence process; large clouds develop to result in rain.

The Solar System

  • Components: Includes the Sun, planets, moons, asteroids, and comets.

  • Formation: From solar nebula 5 billion years ago due to gas clouds and dust (mostly hydrogen and helium).

Life Cycle of Stars

  • Star Formation: Nebula --> Protostar --> Star with nuclear fusion.

  • Lifecycle Sequences: Vary by mass (low mass to red giants and high mass to supernovae).

  • Black Holes: Form from collapsing supergiant cores, possesses an event horizon, and no escape for matter or light.

Galaxies and the Universe

  • Galaxies: Assemblages of stars and gas, with the Milky Way being spiral.

  • Big Bang Theory: Universe's origin with ongoing expansion; supported by cosmic background radiation and element abundance measurements.

    • Hubble's Law: Discovered relationship between galaxy distance and redshift, leading to estimates of the universe's age.