One of the most mysterious places in the Solar System is right underneath your feet: the interior workings of the Earth. Since it's impossible to drill down more than a few km under the surface of the Earth, scientists have study how sound waves from earthquakes travel throughout the planet and get reflected as they bump into things. These sound waves have always acted differently than predicted in simulation. Scientists now think that iron, crushed under tremendous pressure, can significantly alter the speed and direction of these sound waves.