Currenly scientists are stumped (atleast that I know of) on how elements heavier than iron formed. This is because stars can't produce elements heavier than iron through fusion. After iron, fusion switches from exothermic to endothermic. Some people think these elements are created with the immense forces in supernovae. But I have trouble imagining enough heavy elements being created in supernovae explosion to account for the abundance of heavy elements. Anyone care to comment?