system
Given the following post, respond as if you're commenting on Reddit:
human
If the deepest we have drilled into earth is 7.5 miles, not exceeding earths crust, how do we have detailed descriptions/illustrations of what the other of the thousands of miles look like? For example earths core, the mantle and inner core.
gpt
Seismic waves. Earthquakes.

When there is an earthquake different waves will move through the earth, through the different parts of the earth, at different speeds and in different ways. We can measure this at different points and begin to paint a picture. What you are seeing on your seisometre took x time longer to be seen compared to the one closer by, so it traveled through at this speed, or was reflected in this way...

We also have other clues. Gravity we can see how strong it is at different points and heights and work out some density calculations, this adds more information, as well as the magnetic field that's produced meaning we'd have some more liquid parts, and volcanos bringing stuff up from deeper underground. 

All of these help paint a picture, and with them together we can deduce what the unseen layers must be.