What evidence did scientists use to figure out that earth inner core is solid rock?
They do not have evidence. In fact most pf things are not even true. The only thing they say they did was put a stick on the ground and with a shockwave they knew what was inside the earth. My opinion is that the core is not what scientists say it is. Due to the fact that we know more about the moon than our own planet.
A seismograph is used to sense seismic waves in the earth. The seismic waves are sent down by scientist and how fast and how straight the line is when the seismograph reads them is how they tell which mineral or if its a liquid or solid. Which is how they know about the inner and outter core, and the mantel.