Geoscientists use to explore the deep layers of the earth that humans can not yet dig down into.

Geo scientists use SEISMIC WAVES to explore the deep layers of the earth. Geologists use seismic waves to explore the inner core of the earth. There are two principal types of seismic waves, the Pressure waves [P] and the Secondary waves [S].
The P waves can go through liquids and solids while the S waves can go through only solids.

Iwould say silver and gold