Plate Tectonics Basics Explained

Tap a term to see what it means.

Tectonic Plates

Large, rigid sections of Earth's outer shell (the lithosphere) that float atop the semi-fluid mantle beneath them and move slowly over geological time, typically just a few centimeters per year.

Divergent Boundaries

Where two plates move apart from each other, allowing magma to rise and form new crust — this process is responsible for creating mid-ocean ridges and, over millions of years, widening ocean basins.

Convergent Boundaries

Where two plates move toward each other, often causing one plate to be pushed beneath the other (subduction), a process responsible for forming mountain ranges, deep ocean trenches, and many volcanoes.

Transform Boundaries

Where two plates slide horizontally past each other, building up stress along the boundary that is periodically released as earthquakes — California's San Andreas Fault is a well-known example.

Continental Drift

The theory, proposed in the early 20th century, that continents were once joined together in a single landmass (Pangaea) and have gradually drifted to their current positions — an idea that plate tectonics later explained mechanistically.

A theory confirmed relatively recently

Although the idea of continental drift was proposed in 1912, it was not widely accepted by scientists until the 1960s, when new evidence about the ocean floor provided a mechanism — plate tectonics — that could actually explain how and why the continents moved.

Frequently Asked Questions

Are all earthquakes and volcanoes caused by plate boundaries?

The vast majority occur at or near plate boundaries, though a smaller number of volcanoes, such as those forming the Hawaiian Islands, occur in the middle of a plate due to a stationary "hot spot" in the mantle below.

How fast do tectonic plates actually move?

Most plates move at a rate of about 2 to 10 centimeters per year — roughly the speed at which human fingernails grow — though this slow movement adds up to dramatic changes over millions of years.