Other than during the crust, the inside with the Earth can't be studied by drilling holes to get samples. As an alternative, scientists map the inside by observing how seismic waves from earthquakes are bent, mirrored, sped up, or delayed by the different layers. Close icon Two crossed traces that https://econopass.com/news/science-technology/earths-inner-core-rotation-slows-down-what-does-it-mean/