What are two types of evidence geologists use to learn about Earth's interior?

Question

What are two types of evidence geologists use to learn about Earth's interior?

Answer 1

Earthquake behavior and volcanic behavior

Answer 2

The primary evidence is from seismic activity by volcanoes, the second is by actual earthquake activity, both cause waves of low frequency sound, ( infra sound ), capable of transmission through the earths crust around the globe, ( it actually rings, like a bell, when these things happen ! ), the echoes of these waves act like a sonar device and a picture can be drawn of the structure of the planet by measuring the changes to the sound wave frequencies, it was this that was used to describe the first major structure of the world, known as the "MoHo"

The "Mohorovicic discontinuity", ( the transition point, where the core becomes liquid under the "mantle" of the surface layers ), there are other discontinuities found since, that are measured by the same technique......

Answer 3

The analyzing of seismic datas recorded during earthquakes and the variation in temperature as we go down to the earth.

Answer 4

Everyone is right about the geophysical aspect.  We use earthquakes and interpret how the waves travel through the earth.

The geochemistry of the volcanic rocks we see at the surface is also another way of interpretting the earths interior.  Isotopes are useful in this regard.  With isotopes, it is possible to distinguish different chemical reservoirs in the mantle and how they interact.  Most of these reservoirs have stayed isolated from each other for millions or billions of years.  

Scientists are also working on whether the core can input some of its chemical aspects into mantle plume volcanism that originates at the core mantle boundary.  This hasn't been conclusively proven, though.