How is the study of the earth's interior an example of indirect observation

There is really nothing to know. All you have to use is context clues and common sense. We know some synonyms for direct are manage and handle. Indirect means not direct, right? And we can't handle or manage earth's interior (core), right? Therefore, the study of earth's interior is an example of indirect observation because we cannot directly manage it.

Cpopulation density

I'm hella smart but i dont know that