Overview
This lecture covers Earth's internal structure and explains plate tectonics, including the history, key evidence, and the different types of plate boundaries.
Earth's Internal Structure
- Earth is composed of compositional (chemical) and mechanical layers.
- The primary compositional layers are the crust, mantle, and core.
- The lithosphere is the rigid, outermost mechanical layer, including the crust and top mantle.
- The asthenosphere lies beneath the lithosphere, is hotter, under more pressure, and behaves in a partially fluid manner.
- The mesosphere is more rigid due to increased pressure.
- The outer core is liquid, made of melted metals.
- The inner core is solid metal, kept solid by immense pressure despite high temperatures.
History of Plate Tectonics
- Alfred Wegener proposed the continental drift theory in the early 1900s, suggesting continents were once joined in a supercontinent called Pangaea.
- Initial scientific rejection changed after discoveries in the mid-1900s, such as magma rising at oceanic ridges and matching earthquake/volcano patterns to plate outlines.
- Fossil evidence also supported continents once being connected.
Plate Tectonics Theory
- The lithosphere is broken into large, slowly moving plates (about 1–2 inches per year).
- Plate boundaries are sites of major geological activity.
Types of Plate Boundaries
- Convergent boundaries: Plates move toward each other; can form subduction zones (volcanoes) or uplift (mountains like the Himalayas).
- Transform boundaries: Plates slide past each other, creating faults and causing earthquakes (e.g., San Andreas Fault).
- Divergent boundaries: Plates move apart, creating rifts or seafloor spreading (e.g., Mid-Atlantic Ridge).
Geological Features from Plate Movement
- Volcanoes form at subduction zones (convergent boundaries).
- Mountain ranges form as plates collide and uplift rock.
- Earthquakes occur at both convergent and transform boundaries.
- Tsunamis can originate from undersea earthquakes.
- Large cracks (rifts) and new oceanic crust form at divergent boundaries.
Key Terms & Definitions
- Lithosphere — Rigid outer mechanical layer of Earth, includes crust and upper mantle.
- Asthenosphere — Ductile, partially fluid layer beneath the lithosphere.
- Mesosphere — More rigid mantle region below the asthenosphere.
- Outer Core — Liquid metal layer inside Earth.
- Inner Core — Solid metal center of Earth, solid due to extreme pressure.
- Plate Tectonics — Theory describing movement of Earth's lithospheric plates.
- Convergent Boundary — Zone where plates move toward each other.
- Transform Boundary — Zone where plates slide past one another.
- Divergent Boundary — Zone where plates move apart.
- Subduction Zone — Area where one plate dives under another at a convergent boundary.
- Seafloor Spreading — Formation of new ocean crust at divergent boundaries.
Action Items / Next Steps
- Review the different types of plate boundaries and the resulting geological features.
- Watch any relevant visuals or revisit specific lecture sections as needed for clarity.