Our universe and all that we know was formed after the Big Bang, the big expansion that gave origin to our universe and all we can see nowadays, like galaxies, stars and planets. The Big Bang was produced about 13 800 years ago. During the three first minutes of the universe, the first elements started to form, who were mainly hydrogen and helium, two light elements that, between the two of them, represented around the 99% of all the elements that there were in that moment in the universe. The remaining 1% was formed by equally light elements, mainly lithium and deuterium.
After some millions of years, this different materials condensed into big gas clouds, inside of which started to form the first stars that would illuminate that dark universe, based on the two elements that the stars continue to use to create themselves nowadays: hydrogen and helium.
This stars, formed about 250 millions of years after the beginning of the universe originated by the Big Bang, were the responsible of creating more elements inside of their nucleus due to the nuclear fusion. In fact, all the elements of our universe have been formed inside the stars.
Determined types of stars, create more elements than other ones. An example would be the yellow dwarfs, which can only can arrive to create oxygen or carbon in his interior, but they cannot arrive to create heavier elements such as iron, which can only be formed in the interiors of the blue giants or bigger stars. All this elements created in the profundities of stars, are those which, accumulating in big quantities, reached to create the planets or the live that is on them.
Then, all the elements in our universe, are formed based on stars, which fusion its elements that they have in their insides, and, then, fusion the elements that they created. This process it’s repeated until, in the case of the blue giants, they arrive to the iron’s production, which consumes energy instead of producing it. Arrived to this point, they explode into a supernova, which, due to high temperatures of the collapse, creates even heavier elements such as gold.
Therefore, we could say that we are dust of star, actually, all the elements in the Earth and in any other planet, come from the elements that the stars have leaved when dying, and that have got together to form all the planets that we know nowadays.