Plate Tectonics Overview

Plate Tectonics

• The theory of plate tectonics describes the large-scale motion of Earth's lithosphere.
• Earth's lithosphere is broken into several large and small plates that move relative to each other.
• These plates are constantly interacting at their boundaries, resulting in various geological phenomena.

Types Of Plate Boundaries

• Divergent Boundaries: Plates move apart, creating new crust. Magma rises to the surface, forming volcanoes and ridges. Examples include mid-ocean ridges and rift valleys.
• Convergent Boundaries: Plates collide. The type of interaction depends on the plate types (oceanic vs. continental). Oceanic crust is generally denser and can be subducted, leading to volcanic arcs or deep trenches. Continental crust is less dense and typically does not subduct, resulting in mountain ranges.
• Transform Boundaries: Plates slide past each other horizontally. Friction creates earthquakes along faults, like the San Andreas Fault.

Theory Of Continental Drift

• Proposed by Alfred Wegener, this theory suggested that continents were once joined in a supercontinent (Pangaea) and have since drifted apart.
• Evidence included the fit of continents, distribution of fossils, and matching rock formations on different continents.
• The theory was initially rejected due to a lack of a mechanism to explain the movement of continents.

Seafloor Spreading

• This process occurs at divergent boundaries. Magma rises from the mantle, creating new oceanic crust along mid-ocean ridges. The newly formed crust pushes older crust to the sides, widening the ocean basin.
• The process provides evidence for the movement of plates.
• Magma emerges from the Earth's mantle, cools, and solidifies into new crust.

Convection Currents

• Convection currents are circulatory movements within the Earth's mantle.
• These currents are driven by differences in temperature and density within the mantle.
• Warmer, less dense material rises, while cooler, denser material sinks.
• This movement plays a crucial role in driving plate tectonics.

Interior of Earth

• Earth's interior consists of layers with varying physical and chemical properties:
  • Crust: The outermost, relatively thin layer, composed of solid rock.
  • Mantle: A thick layer beneath the crust, mostly solid rock but may exhibit some viscous flow. Its composition is largely silicate minerals.
  • Outer Core: A layer of molten iron and nickel.
  • Inner Core: A dense, solid ball of iron and nickel.
• The different layers interact through convection currents within the mantle, impacting plate movement. These differing densities and viscosities are essential for the process of plate tectonics to occur.