Lesson 3: Earth's Plates

Key Idea

While the Earth's outer layer is made of solid rock everywhere, it is not one unbroken piece like an eggshell. Instead, it is fractured into massive, interlocking sections called tectonic plates.

These plates vary in size and shape, fitting together to cover the entire planet. Both continents and ocean floors ride on top of these huge slabs of rock. Understanding that the Earth is a puzzle of separate sections is key to understanding geological events.

Key Idea

Geologists define the edges of these plates by mapping geologic events. When scientists plot the location of earthquakes on a map, they do not appear randomly; they form long, distinct lines.

These lines of seismic activity reveal the plate boundaries. Because the plates are separate pieces, they interact at their edges. This interaction causes shaking, effectively tracing the outline of each plate and allowing scientists to map Earth's hidden structure.