system
Given the following post, respond as if you're commenting on Reddit:
human
How exactly did we find out about Earth’s internal layers if we never dug that deep?

  The crust, mantle, and core.
gpt
Mainly by analyzing seismic waves. It's basically like taking an ultrasound of the Earth, using earthquakes as the sound source. Computer models are also helpful. And finally, looking at mineral samples on the surface can provide information about the conditions in the mantle under which they were formed.