Our modern model of the Earth consists of
layers, illustrated in Figure 1. The major divisions are the
crust, the mantle, the inner core, and the outer core. But how
do we know that the Earth's layers exist? What magic allows us
to see into the Earth? To answer this question, we will follow
the history of seismology from Emil Weichert, who proposed that
the earth is made of layers in 1896, to Inge Lehmann who's
analysis of seismic waves from an earthquake on the other side
of the planet lead to the conclusion that the Earth's outer core
is liquid. Figure 2 is a summary of the major events along the
way!
Figure 1. Taken from https://geology.com/articles/mohorovicic-discontinuity.shtml
Figure 2. Taken from https://www.iris.edu/hq/inclass/animation/layers_of_the_earth
Background taken from: transparenttextures.com