It’s a common elemental theme we see across stories, fantasies, etc. It seems like it is an element that should be part of that pantheon but maybe there is a scientific explanation of why it isn’t? Or is it simply, they did not have enough understanding of it at the time those 4 were suggested.
Could be fun.
Long ago, the 118 nations lived together in harmony. Then, everything changed when the Ytterbium Nation attacked.