Physical Geography · StudentHub Lesson
Plate Tectonics
Earth's lithosphere is broken into moving plates whose interactions build mountains, cause quakes, and shape continents.
What you will learn
- Describe the structure of the Earth's layers
- Explain the theory of continental drift and plate tectonics
- Identify the three types of plate boundaries
- Explain how plate movement creates landforms and hazards
- Give real-world examples of plate boundary features
Watch the lesson
The Plate Tectonics Revolution: Crash Course Geography #19 · CrashCourse
Watch on YouTubeTopic notes
Main Idea
The Earth's outer shell is broken into large rigid plates that float on the semi-molten mantle and move slowly over time, driving the creation of continents, oceans, and mountains.
Key Concepts
- Earth is made of layers: crust, mantle, outer core, inner core.
- The lithosphere (crust + upper mantle) is split into tectonic plates.
- Alfred Wegener proposed continental drift; Marie Tharp's ocean floor mapping and Fred Vine's seafloor spreading evidence confirmed plate tectonics.
- Convection currents in the mantle drive plate motion.
Definitions
- Plate boundary: the edge where two plates meet.
- Divergent boundary: plates move apart (e.g., mid-ocean ridges).
- Convergent boundary: plates move toward each other (subduction or collision).
- Transform boundary: plates slide past each other (e.g., San Andreas Fault).
Processes
- At divergent boundaries, magma rises to create new crust.
- At convergent boundaries, one plate may subduct beneath another, forming trenches and volcanoes, or two continental plates collide to form mountains.
- At transform boundaries, friction builds and releases as earthquakes.
Real-World Examples
- The Mid-Atlantic Ridge is a divergent boundary.
- The Himalayas formed from the collision of the Indian and Eurasian plates.
- The San Andreas Fault in California is a transform boundary.
Common Mistakes
- Confusing continental drift (Wegener's original idea) with the fully developed theory of plate tectonics.
- Thinking plates only move at the edges of continents, not oceans too.
- Assuming all volcanoes and earthquakes happen randomly rather than at predictable boundary zones.
Key concepts
Important terms
- Subduction
- The process where a denser tectonic plate sinks beneath a less dense one at a convergent boundary.
- Continental drift
- Wegener's hypothesis that continents were once joined and have since drifted apart.
- Seafloor spreading
- The process by which new oceanic crust forms at mid-ocean ridges as plates diverge.
- Lithosphere
- The rigid outer layer of Earth made up of the crust and uppermost mantle.
Quick revision
- Earth has crust, mantle, outer core, inner core
- Lithosphere is broken into tectonic plates
- Wegener proposed continental drift
- Tharp mapped the ocean floor revealing ridges
- Divergent boundaries create new crust
- Convergent boundaries destroy crust or build mountains
- Transform boundaries cause earthquakes
- Mid-Atlantic Ridge is divergent
- Himalayas formed by continental collision
- San Andreas Fault is transform
Check your understanding
Question 1 · Multiple choice
What causes tectonic plates to move?
Question 2 · Multiple choice
Which type of boundary forms the Himalayas?
Question 3 · True or false
At a divergent boundary, new crust is created.
Question 4 · Short answer
Name the scientist who proposed continental drift.
Question 5 · Short answer
What is the name of the boundary type found at the San Andreas Fault?
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