Overview
This lecture explains the basics of plate tectonics, how the Earth's surface is made of slowly moving plates, the types of plate boundaries, and how these processes shape continents and cause earthquakes.
Plate Tectonics Basics
- Plate tectonics describes the movement of large sections (plates) of Earth’s outer layer.
- The Earth's surface moves slowly, generally 1-6 inches per year, making movement hard to feel.
- Rapid, noticeable movement is experienced during earthquakes, which are rare.
Structure of the Earth
- The Earth has several layers, from the crust down to the core.
- The lithosphere is Earth's top layer, made up of the crust and upper mantle.
- The lithosphere is divided into tectonic plates.
- Beneath the lithosphere is the asthenosphere, a hot, molten, and movable layer.
Tectonic Plates
- Plates float on the molten asthenosphere, similar to ice cubes on water.
- There are 7 major and 10 minor tectonic plates.
- Plates are up to 62 miles thick and can cover entire continents.
- Plates are classified as oceanic (sema: silicon and magnesium) or continental (cla: silicon and aluminum).
Plate Boundaries
- Most movement occurs at plate boundaries, which are the meeting points of plates.
- Convergent boundaries: Plates move toward each other; one slides under another (subduction), forming mountains, volcanoes, and earthquakes (e.g., Mount Everest, Mariana Trench).
- Divergent boundaries: Plates move apart, forming rift valleys and ridges (e.g., East African Rift Valley, Mid-Atlantic Ridge).
- Transform boundaries: Plates slide past each other, causing earthquakes (e.g., San Andreas Fault).
Continental Drift and Pangaea
- Continents were once joined as a single landmass called Pangaea.
- Plate tectonics slowly separated Pangaea into the continents we see today.
Modern Technology and Plate Movement
- Scientists use GPS to monitor plate movements and attempt to predict earthquakes.
Key Terms & Definitions
- Lithosphere — Earth's rigid outer layer, including the crust and upper mantle.
- Asthenosphere — The semi-fluid layer beneath the lithosphere that enables plate movement.
- Tectonic Plates — Large sections of the lithosphere that move over the asthenosphere.
- Subduction — Process where one plate moves under another at a convergent boundary.
- Rift — A gap formed at a divergent boundary.
- Pangaea — The ancient supercontinent that broke apart to form today’s continents.
Action Items / Next Steps
- Review diagrams of plate boundaries and major/minor tectonic plates.
- Optional: Research recent earthquakes and identify their boundary types.