How were the heavy elements from iron to uranium made?

Unlike light elements, which release energy during fusion, elements heavier than iron require energy for their creation. This happens because the nuclear binding energy is at its maximum at iron. Hence lighter elements were made in ordinary stars, using fusion. read more

Stars release energy mostly produced by Hydrogen fusing into Helium. As a star becomes older, there is less Hydrogen so it starts fusing heavier elements. But each time you move along the periodic table, less and less energy is produced. read more

both dark matter and possibly dark energy originate from the earliest days of the universe when light elements such as helium and lithium arose heavier elements formed later inside stars where nuclear reactions jammed protons read more