Structure of the Earth

Caitlin Dempsey


Listed here are quick facts about the Earth’s crust, mantle, and core.


The crust the outer layer of the Earth varying between 5 to 50 km in depth under the surface of the earth.  The crust is the outermost and thinnest layer of the earth’s surface. The crust comprises about 5% of the earth body.  

The thickness of the crust is more under the continents and lesser under oceans. The outermost layer of the crust is composed of lighter silicates termed as sial (Silica +Aluminium).  Moho or Mohorovicic discontinuity separates crust from mantle.

A detailed graphic showing the location of the Earth's crust, mantle, and core.
Cutaway images of the Earth’s interior structure. Left: A scale graphic demonstrates how thin the Earth’s crust is. Right: A not-to-scale view of the Earth’s crust, mantle, and core. Image: USGS, public domain.

Where the Earth’s Crust is Visible

Ophiolite is a landform characterized by the presence of ancient oceanic crust at the land surface. The mountains of northeastern Oman were once found below the ocean floor. Located in the Hajar Mountains of Oman, the Semail (or Samail) ophiolite is visible in this satellite image captured  on March 6, 2012.

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In this EO-1 satellite image, rocks progress from west to east (left to right) from the deepest parts of the earth to those that were originally exposed on the ocean floor starting with peridodites that were once part of the Earth’s mantle and progressing to various rocks that emerged from the crust.

A satellite image of ophiolite in Oman.
A satellite view of the Semail (or Samail) ophiolite in Oman. Image: EO-1, NASA, public domain.


The mantle is the portion of the earth that is made up of iron and magnesium silicates, with temperature ranging up to 16000 C and extends downwords to a depth of about 1000 km. The thickness of the lower mantle is about 1900 km.  

The mantle contains 83% of the total volume and 68% of the total mass of the earth.  The mantle is separated from the core by Gutenberg discontinuity. It is largely composed of silicon and magnesium called sima. The rocks in this layer may be in the glassy state.


There are two parts of the earth’s core.  The outer core, approximately 2100 km thick, consists of molten iron and nickel with temperatures ranging between 20000 C and 50000 C. Below this is the solid inner core which has diameter of 2,740 km.  

A diagram showing the Earth's inner and outer core.
The Earth’s core. Image: NASA/JPL, public domain.

The core is the central region of the earth. It is 3475 km in radius. By volume, it is 16% of the earth body . By mass, it constitutes 32% of the mass of the earth. The temperature of the inner core is 60000 C – 70000 C.

The inner core is composed of NiFe (Ni for Nickel Fe for Iron.).


Scott, M. (2012, March 31). Earth’s Crust Exposed In Oman. Earth’s Crust Exposed in Oman.

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About the author
Caitlin Dempsey
Caitlin Dempsey is the editor of Geography Realm and holds a master's degree in Geography from UCLA as well as a Master of Library and Information Science (MLIS) from SJSU.