The two substances are rock (molten and solid) and metal (solid + liquid).
Layers of the earth from the outside in:
1. crust. hard rock/dirt/ground. Shell
2. mantle. melted rock and stuff. Egg white
3. core. Outer core - liquid. Inner core- solid. Nickle and iron. Yolk
Im pretty certain it is volcanic eruption
<span>Some bacteria in the soil fix nitrogen into useful forms for plants to use them. This conversion of nitrogen helps plants grow. Without the bacteria in the soil a lot of the plants would not be able to grow.</span>