Arcana is the collective energies left over from the creation of the earth. It allows mankind to wield powers beyond their normal abilities. The Silent Gods sealed it away after banishing Jenova to the furthest regions of nothingness. Without magic, mankind found themselves in a primitive state, which they were able to survive with the development of technology much later. When Jenova escaped the nothingness she was cast into, she killed the Silent Gods, who had long ago dropped their guard. When Aracana was awoken by Jenova, it destroyed most complex electronics and machinary, and changed large portions of the earth back to its distant past.