Air + Earth = Dust
Earth + Fire = Lava
Air + Fire = Energy
Water + Earth = Mud
Water + Air = Rain
Earth + Rain = Plant
Fire + Water = Steam
Air + Lava = Stone
Stone + Fire = Metal
Metal + Stone = Blade
Blade + Stone = Tool
Tool + Stone = Axe
Axe + Tree = Wood
Wood + Tool = Wheel
Wheel + Wheel = Cart
Cart + Cart = Train
Train + Time = Time