What did the Soviets discover in the Kola Superdeep well at a depth of 12,262 meters?

We know so little about the structure of the Earth. For example, our planet is not fully spherical, as it slightly flattens when rotating. Therefore, its equatorial diameter (12.754 km) is 43 km larger than the polar one (12.711 km). Our planet is the densest celestial body in the solar system, followed by Mercury among other planets. Different layers of our planet's core, crust, and mantle rotate at different speeds relative to each other. Oxygen makes up about 50% of the entire earth's mass