An atom is a tiny building block that all matter is made up of. Every atom has a core (or "nucleus") made of protons and neutrons, with electrons orbiting the nucleus in a cloud. This structure is often illustrated with colored spheres for easier understanding.
The rock cycle is the constant transition of the world's rocks due to erosion, heat, and pressure. As rocks wear away, melt, and freeze, they transition between the three major rock types: Igneous, Sedimentary, and Metamorphic.
Interestingly, I just saw this picture of Saturn from the Cassini probe that is eerily similar to how I had imagined the same view. While I hadn't seen the photograph until a couple days after I had done the artwork, the real picture was actually taken over a year ago.