The
inner Earth is inaccessible. Unlike the surface, where we can collect rocks
and study them directly, further than a few kilometres in we can only deduce
the geology through physical reasoning and experiment. This part of the web
site gives a guide to how we can establish the geological nature of the inner
Earth. We can start by establishing the shape and size of the Earth (it
is not a perfect sphere). We can apply Newton's Law of Gravitation to estimate
the mass and density of the Earth.
To establish how this mass is distributed - and thus get a first idea of the
inner structure - we must establish the Moment of
Inertia. All this allows us to deduce that there is a crust, mantle and
core.
To get more information we must use the science of seismology - studying how
seismic waves (especially from earthquakes) are transmitted. Different waves
are transmitted with different velocities. Measuring the travel time of seismic
waves from source (earthquake focus) to receivers distributed
around the Earth can be used to establish the classical
layered structure - confirming the models of Earth structure deduced from
gravity and orbit.
