Inner Core of the Earth: Definition, Composition & Facts

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  • 0:01 Formation and Composition
  • 0:19 Temperature
  • 0:35 Studying the Inner Core
  • 2:45 Lesson Summary
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Lesson Transcript
Instructor: Jeff Fennell

Jeff has a master's in engineering and has taught Earth science both domestically and internationally.

The inner core is located at the center of the Earth and is composed of nickel and iron. Most of what we know about the inner core is through studying seismic waves. This lesson will cover the facts about the inner core.

Formation and Composition

According to the nebula formation theory, Earth was formed from a cloud of gas of various elements. As the cloud condensed, it is believed that the heavier metals sank to the center. The inner core is believed to consist of these heavier elements, primarily nickel and iron.


The temperature of the inner core can only be determined indirectly from seismic activity and computer models, and it is currently believed that the temperature is about 9,800 degrees F. While in most circumstances, this would result in iron acting as a liquid, the intense pressure of the earth causes iron to act as a solid.

Studying the Inner Core

Although we have never physically been to the inner core, we can use indirect methods to determine its properties. When an earthquake hits, seismic waves are released and travel through the earth. There are two types of seismic waves, primary and secondary. Both types travel out radially away from the epicenter.

Of the seismic waves, only primary waves can travel through all layers of the earth. It's this property of primary waves that has given us a peek into the earth's center. Throughout the 20th century, seismographs, or instruments designed to record seismic waves, were positioned around the globe to better understand seismic waves.

Earthquakes occurred, and the seismographs worked as they were supposed to, recording the primary waves. To the surprise of scientists, however, there were two distinct areas on the earth that wouldn't record primary waves. Primary waves were recorded on seismograms up to 110 degrees away from the epicenter and remained absent until 150 degrees when they would reappear. This is known as a seismic shadow zone, and it provides geologists insight into the properties of the inner core.

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