Plate Tectonics Overview

Plate Tectonics

• Plate tectonics is a theory that describes large-scale motions of Earth's lithosphere.
• It explains the formation, movement, and interaction of Earth's plates.
• The theory was developed after years of observing that continents appeared to move over time.

Types of Plate Boundaries

• Divergent boundaries: Plates move apart, creating new crust. Magma rises to the surface, forming new oceanic crust. Examples include mid-ocean ridges.
• Convergent boundaries: Plates collide, leading to subduction (one plate moving under another) or mountain building. Oceanic-continental convergence can create volcanoes. Oceanic-oceanic convergence creates volcanic island arcs. Continental-continental convergence builds mountain ranges.
• Transform boundaries: Plates slide past each other horizontally, causing friction and earthquakes. Famous examples are the San Andreas Fault.

Theory of Continental Drift

• Proposed by Alfred Wegener, this superseded theory posited that continents were once joined in a supercontinent called Pangaea.
• Evidence supported the idea of continental drift as it detailed similar fossils, rock types, and geological structures on continents now separated, suggesting a past connection.

Convection Currents

• These are slow, circulating movements of the mantle's semi-molten rock (magma/asthenosphere).
• Driven by differences in temperature and density, hot material rises, cools, and sinks, creating a cyclical pattern.
• This movement is considered a key driving force of plate tectonics.

Seafloor Spreading

• This process occurs at mid-ocean ridges where new oceanic crust forms as magma rises to the surface and solidifies.
• As new crust forms, older crust moves away from the ridge.
• The age of the seafloor progressively gets older as you move further away from the mid-ocean ridge.
• The mechanism for seafloor spreading is driven by convection currents in the mantle.

Interior of Earth

• The Earth has progressively denser layers as you go from the outer crust to the inner core.
• The crust is the outermost solid layer composed of different rock types.
• The mantle is a thick, semi-molten layer of rock beneath the crust, crucial for convection.
• The core is composed of iron and nickel, with a solid inner core and a liquid outer core. The liquid outer core generates Earth's magnetic field.
• Each layer has distinct properties concerning composition, temperature, and pressure.