Final answer:
Scientists use seismic waves, laboratory simulations, volcanic sample study, and geophysical measurements to determine Earth's interior layers.
Step-by-step explanation:
Scientists use a variety of innovative tools to understand the depths and composition of Earth's layers. Seismic waves generated by earthquakes are a primary tool used to explore Earth's interior. These waves travel through the Earth and are recorded by seismographs. Variations in wave speed and the bending of wave paths (refraction) as they travel through different materials provide insight into the depth and density of layers. Additionally, laboratories replicate the high pressure and temperature conditions found inside Earth to understand the behavior of materials and support seismic data findings. Other methods include studying rocks that come from deep within the Earth, like those brought to the surface by volcanic activity, and making inferences from the Earth's magnetic field and gravity field measurements.