Water Element:<br/>I would use the wide availability to water to make the oldest legends about it being a passage between the realm of the living and the realm of a spirit into a reality. In much the same way that alice steps through the looking glass, the average person would be able to step into a pool of water anywhere in the world and enter into a realm of gentle dreams or vicious nightmares.<br/><br/>Fire Element:<br/>I would infuse the elemental power of fire into chunks of obsidian to create an efficient power source for a variety of personal, professional and military grade weapons and armaments. I would also make it so that anyone who tried to burn ants, pill bugs, etc would instead force feed that insect an intense amount of energy that would make them grow exponentially in size so that the bug could face its attacker on even ground.<br/><br/>Air Element:<br/>I would shape the clouds and the storms into herds of horses that one could mount and race across the heavens with.<br/><br/>Earth:<br/>I would open a vast cavern deep within the earth and fill it with the light of heaven. Here, within the very heart of the world, the most ancient and perfect spirits of all creation would reside and help shape the ongoing fate of humanity and the world.