Earth's Layers and Tectonic Plates

Earth is made up of four distinct layers, each with different properties. Scientists have learned about these layers by studying earthquake waves that travel through the planet. Understanding Earth's structure also helps us explain earthquakes, volcanoes, and the formation of mountains.

The Four Layers of the Earth

• Crust — the thin, solid outer layer where we live. It is divided into large pieces called tectonic plates.
• Mantle — the thick layer beneath the crust, made of hot rock that is mostly solid but flows very slowly. It is the thickest layer and drives tectonic plate movement.
• Outer Core — a layer of liquid iron and nickel surrounding the inner core. Its movement generates the Earth's magnetic field.
• Inner Core — the solid center of the Earth, made mainly of iron and nickel. It is the hottest part of Earth, yet stays solid due to enormous pressure.

Tectonic Plates

• Tectonic plates are large pieces of the Earth's crust that float on the mantle.
• Plates move very slowly — only an inch or two per year (a few centimeters).
• This movement causes earthquakes, volcanoes, and the formation of mountains.

Effects of Plate Movement

• Collision — when two plates push against each other, mountains form.
• Separation — when two plates move apart, new crust forms as magma rises.
• Sliding — when two plates slide past each other, earthquakes occur.