Why do less dense compounds make up earths crust while the densest compounds make up the core

Bc the more dense the stronger they are so they would be at the center. it is like you wouldn't put the heavier that the top you would put it at the bottom to hold the lighter up . so its the same thing you wouldn't put the lighter, less dense, in the middle and the heavier, more dense, on the outside bc it would just crumble.

They are like other investigations? say there was a murder u have to do blood test and finger prints which run through a lab.