Layers of the Earth

How were Earth’s layers discovered? What are they?

Earth’s interior is broadly grouped into three main layers on the basis of chemical composition: crust, mantle, and core. An egg analogy is used to show relative thicknesses, and a Big Hunk analogy illustrates how a material of a single composition can be either brittle or ductile depending on temperature. This animation shows briefly how scientists figured out where these layers were, what the layers are, and how the crust is often mistaken for the tectonic (aka lithospheric) plates.


Keypoints:

  • Layers were deduced by Sir Isaac Newton (1700) to Inge Lehmann (1937)
  • Earth’s 3 main layers: crust, mantle, core
  • Layers are defined by composition
  • Each layer has physical variations due to temperature and pressure
  • The crust is only the upper part of the tectonic (lithospheric) plate. 

Related Lessons

Learning occurs as students work first in small groups and then as a whole class to compare predicted seismic wave travel times, generated by students from a scaled Earth model, to observed seismic data from a recent earthquakes. This activity uses models, real data and emphasizes the process of science.

Related Fact-Sheets

Earthquakes create seismic waves that travel through the Earth. By analyzing these seismic waves, seismologists can explore the Earth's deep interior. This fact sheet uses data from the 1994 magnitude 6.9 earthquake near Northridge, California to illustrate both this process and Earth's interior structure.

Related Interactives

Roll over the buttons to see the difference between P- and S-wave seismic paths as well as their respective shadow zones.

Related Animations

Seismic tomography is an imaging technique that uses seismic waves generated by earthquakes and explosions to create computer-generated, three-dimensional images of Earth's interior. Human CAT scans are often used as an analogy. Here we simplify things and make an Earth of uniform density with a slow zone that we image as a magma chamber.

A travel time curve is a graph of the time that it takes for seismic waves to travel from the epicenter of an earthquake to the hundreds of seismograph stations around the world. The arrival times of P, S, and Surface waves are shown to be predictable. This animates an IRIS poster linked to this animation.

Related Posters

Seismic waves from earthquakes ricochet throughout Earth's interior and are recorded at geophysical observatories around the world. The paths of some of those seismic waves and the ground motion that they caused are used by seismologists to illuminate Earth's deep interior.