The Structure of the Earth

The Earth is made up of several layers, each with different materials and properties. The three main layers are the crust, the mantle and the core. Understanding the Earth's interior is a basic part of physical geography in exams.

The Crust

• The crust is the outermost and thinnest layer.
• It is thicker under continents and thinner under oceans.
• The upper part is called SIAL (silica and aluminium).
• The lower part is called SIMA (silica and magnesium).

The Mantle

• The mantle lies below the crust.
• It extends to a depth of about 2,900 kilometres.
• It contains the semi-molten asthenosphere where magma forms.

The Core

• The core is the innermost layer.
• It is mainly made of iron and nickel, called NIFE.
• The outer core is liquid and the inner core is solid.
• The core is the hottest part of the Earth.

Boundaries Between Layers

• The Mohorovicic discontinuity separates the crust and mantle.
• The Gutenberg discontinuity separates the mantle and core.

Quick Revision Points

• The Earth has three layers: crust, mantle and core.
• The crust is the thinnest layer.
• The upper crust is SIAL; the lower crust is SIMA.
• The core is made of iron and nickel (NIFE).
• The outer core is liquid; the inner core is solid.
• The mantle goes down to about 2,900 km.
• The Moho separates crust and mantle.