How do scientist really know about the Earth's curst? What type of tools do they use to find this stuff out?

Question

Magnets? Scopes? Radars? Machines? Theories? How do they know?

Answer 1

Earthquakes.  They use instruments called seismographs and lots and lots of earthquakes.  Earthquakes release energy which travels as waves.  Two main types of waves.  These waves travel at different speeds through different substances.  There are thousands of seismographs around the world.  Lots of earthquakes provide lots of data.  Together the varying arrival time of earthquake waves have allowed geologists to come up with a good profile of the planet.  

Smaller areas can be studied with waves produced from artificial sources.  Ground thumping devices or small explosions are used.  Smaller areas can be studied with ground penetrating radar systems.  I confess I'm rather out of date in regards to these matters.  Hopefully someone with a more recent education can help you more.

Perhaps the people who gave me a thumbs down can share their wisdom and tell me where I made a mistake.  Are earthquakes no longer the primary source of P and S waves for seismograph interpretation?  Has something changed.  Are ground penetrating radars now applicable for regional as opposed to local surveys.  I admitted I'm out of date.  Please tell us what has changed to make my answer incorrect.