When were the heavy metals in earth formed?

The process of nuclear fusion, in which two hydrogen atoms fuse together to form one helium atom, etc., continues until iron is formed, at which point stars the size of our sun eventually run out of hydrogen and begin to burn helium, turning into red giants.

However, there are many stars that are far bigger than our sun. For example, one star is 1300 times bigger than our sun, but it will live and die in a relatively short time because a star's life is inversely related to its size.

During the final stages of their lives, these massive stars expand outward and undergo a phase known as a supernova before collapsing in on themselves. The cause of this is gravity, of course, but the nuclear fusion that has been occurring all along also results in the formation of iron and other natural elements. Metals like gold, silver, platinum, uranium, and other heavy metals are formed in these super novae.

Many of these heavy metals are released into space when that star finally explodes, eventually finding their way to other stars in their constellation.

The nucleosynthesis processes in stars, mainly through stellar fusion reactions and supernova explosions, produced the heavy metals that are present on Earth billions of years ago.