Lecture 2, titled “Plate Tectonics: The Big Picture; Part 1,” focuses on the basic data and mechanisms behind the movement of Earth’s surface.
1. Earth’s Internal Structure
The lecture distinguishes between two ways of classifying the Earth’s interior:
• Compositional Classification: Based on what the layers are made of, consisting of the Crust, Mantle, and Core.
• Mechanical Classification: Based on how the layers behave. The Lithosphere (0–100 km depth) is strong and rigid, while the Asthenosphere (100–200 km depth) is mechanically weak and partially molten.
2. Mapping the Earth’s Surface
Geologists use specific terms to describe the distribution of elevations:
• Topography: Elevations above sea level.
• Bathymetry: Depths below sea level.
• Key Features: Major surface features include mid-ocean ridges (which can be 2–3 km tall), deep ocean trenches (6–11 km deep), and island arcs like Japan.
3. Evidence for Plate Tectonics
Tectonic activity—defined as earthquakes, volcanism, or mountain building—is not random but occurs in distinct belts. These belts of activity divide the lithosphere into tectonic plates. Additional evidence comes from magnetic stripes on the seafloor, which record magnetic reversals (the flipping of Earth’s magnetic field) as new oceanic plates are created.
4. Plate Boundaries and Mechanisms
There are three primary types of relative motion at plate margins:
• Divergent: Plates move apart, typically at mid-ocean ridges where new crust is formed.
• Convergent: Plates move toward each other.
• Transform: Plates slide horizontally past one another.
The fundamental driver of this movement is convection. Driven by escaping heat from the Earth’s interior, rock material at the bottom heats up, becomes less dense, rises, cools at the top, and then sinks again in a continuous cycle.
5. Course Expectations and Deadlines
The lecture also served as a reminder of upcoming responsibilities:
• iClicker: Students must register their iClicker Cloud account via Brightspace; the first questions for points begin in Lecture 4.
• Connect Assignments: The first few assignments (Connect 2-4) are due 30 minutes before Lecture 4.
• Quizzes: Post-lecture quizzes 1-4 must be completed by 11:59 PM on January 26th.