Overview
This lecture explains how earthquakes, volcanoes, and mountain ranges are distributed globally, focusing on Earth's lithosphere, plate boundaries, and their relation to the Pacific Ring of Fire.
Earth's Lithosphere Structure
- The lithosphere is Earth's outer layer, including the crust and the upper part of the mantle.
- The crust is made of solid rocks: sedimentary, metamorphic, and igneous.
- Crust thickness ranges from 5 to 50 kilometers; its average density is 2.8 g/cm³.
Types of Crust
- Oceanic crust is denser, made mostly of basalt, 5–10 km thick, and generally younger.
- Continental crust is less dense, made mostly of granite, 30–50 km thick, and consists of older rocks.
- Both types are solid, composed of rock, form tectonic plates, and are part of the lithosphere.
Plate Tectonics and Plate Boundaries
- Earth's lithosphere is broken into tectonic plates that move as single units over the mantle.
- The map of plate boundaries uses broad lines to show where plates meet and interact.
- Scientists use the locations of earthquakes, volcanoes, and mountain ranges to mark plate boundaries.
Distribution of Earthquakes, Volcanoes, and Mountains
- Earthquakes often start at or near plate boundaries.
- Most active volcanoes and mountain belts are found along these boundaries.
- The Philippines and other regions along the Pacific Ring of Fire frequently experience tectonic activity.
Key Terms & Definitions
- Lithosphere — Earth’s rigid outermost layer, including the crust and part of the upper mantle.
- Crust — The outer solid rock layer of Earth; includes oceanic and continental types.
- Tectonic Plates — Large, moving pieces of Earth's lithosphere.
- Plate Boundaries — Regions where two tectonic plates meet and interact.
- Pacific Ring of Fire — Area around the Pacific Ocean known for frequent earthquakes and volcanoes.
Action Items / Next Steps
- Review figures/maps showing the distribution of earthquakes, volcanoes, and mountain ranges.
- Prepare to discuss how plate movement affects geological features in the next lesson.