Planetary-scale geological processes, such as mantle convection and geodynamo action, operate at great depths and are governed by the physical properties of the mantle and core. However, available information on the deep Earth’s physical properties is insufficient for a detailed understanding of how our planet works. Within the CLEAR Young Investigators Group at GFZ, we use state-of-the-art spectroscopic techniques to study how minerals and rocks interact with light at high pressures and temperatures. Our novel approach allows overcoming severe experimental challenges and offers unique insights into the physical properties of geomaterials at extreme conditions.