Ask A Scientist General Science Archive

Question:  How did they discover the Earth's layers?
 d c whitbeck

Answer:
The Earth's layers were discovered by looking at recordings
of seismic waves generated by earthquakes.  When an earthquake
occurs, seismic waves travel throughout the earth.  It is
these seismic waves that cause the ground to shake near an
earthquake.  At great distances these waves can no longer
be felt, but sensitive seismic instruments can still record
them.  Today's instruments are so sensitive that even moderate
size earthquakes (magnitude 5) can be recorded on the other
side of the world.

By looking at the recordings made by seismic instruments, scientists
can deduce what the interior of the Earth looks like.  This is
much the same method as a CAT-scan used by doctors to image
the brain.

The layers of the Earth were discovered during the first half
of this century after modern seismographs were invented.  Scientists
are still studying the details of the constitution of the Earth
in this way.
-Grant