Final answer:
Scientists gain knowledge about Earth's solid and liquid layers through seismic imaging and by studying Earth's magnetic field. Seismic imaging involves monitoring of seismic waves, while the study of the magnetic field is related to the moving material in Earth's liquid metallic core.
Step-by-step explanation:
Scientists primarily learn about the solid and liquid layers of Earth via seismic waves and by understanding Earth's magnetic field. The process involves seismic imaging, where the seismic waves which travel through Earth due to earthquakes or explosions are monitored at different locations. These waves interact differently with varying materials, some of these travelling along the surface and others passing through the interior. This difference in travel paths helps construct a model, revealing the distinct layers of solid and liquid materials within Earth's interior.
Apart from seismic waves, another crucial piece of information about earth's interior is brought about by studying its magnetic field. Earth behaves as though a massive bar magnet lies within it, which is assumed to be produced by moving material in its liquid metallic core. This circulated electric current within the moving liquid metal results in a magnetic field, which further helps distinguish between the liquid and solid layers of earth.
Learn more about Study of Earth's Interior