During the formation of the solar system Earth underwent an event known as the late bombardment. This was a time of a high amount of asteroid collisions hitting the Earth’s surface. These objects painted the surface of our planet with heavy elements such as gold, silver and titanium.
But how did these asteroids form and where do they come from? Scientists still don’t know the full answer to this question. The issue here is that even our Sun can only produce up to a certain level of heavy materials. Star power works because atoms of hydrogen combine to form helium, but the size and density of most stars can only produce Iron until they lose power and collapse.
One theory is that the biggest stars in our universe live these short lifespans. When they die they explode and produce these very dense stars known as neutron stars. The explosion itself is known as a supernovae and in this event it is thought that there is enough heat to produce heavy elements.
However even with this scenario, the computer models are not completely conclusive and so Enrico Ramirez-Ruiz at UC Santa Cruz has been developing alternative theories.