Final answer:
Scientists use seismic waves produced by earthquakes and seismographs to study Earth's internal composition, revealing the core, mantle, and crust's structure.
Step-by-step explanation:
Scientists study the interior of the Earth primarily through seismic waves generated by earthquakes. These waves travel through Earth's layers and are tracked using a network of seismographs, allowing researchers to create a model of Earth's interior structure, including the core, mantle, and crust. Seismic waves are like sound waves, altering in speed and direction as they move through different materials, which vary in density and state (solid or molten). As waves get reflected and refracted, scientists interpret these variations to inform them about the various internal layers, illustrated by seismic studies.