Scientists know it as the Big Bang, the great explosion that created the universe. While dimmed, it's fire has never gone out, and no matter where you are, you can still detect its residue radiation waiting for the Big Crunch to refuel the cosmic fire. Since the Universe was created from flame, it follows that everything in it contains flame. This is the the second teaching of the Church. This is easily demonstrated.
Some materials are closer to the flame than others.
From this basic truth, we can derive the Hierarchy of Flame. Every material has it's place in the Hierarchy. They are arranged by the intensity of the flame produced. Hence first on the list is the Proton, which by changing its mass in the fusion process releases the purest form of energy. Also on this list are the radioactive elements, headed by those, such as Uranium 235 and Plutonium, that allow a chain reaction to take place.