Question

How were the heavy elements from iron to uranium made?

Answer 1

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 and neutrons together to make new atomic nuclei. For instance, four hydrogen nuclei (one proton each) fuse through a series of reactions into a helium nucleus (two protons and two neutrons). That's what happens in our sun, and it produces the energy that warms Earth. 

Answer 2

Hlo mate,

your answer is here,

The elements formed in these stages range from oxygenthrough to iron. During a supernova, the star releases very large amounts of energy as well as neutrons, which allows elements heavier than iron, such as uranium and gold, to be produced. In the supernova explosion, all of these elements are expelled out into space.