Supernova

We are all made of stardust.  Literally.  Almost every element required for life, such as carbon, oxygen, nitrogen and iron, were created in the cores of super massive stars.

The early universe was very hot and consisted mostly of Hydrogen and some Helium. As the universe cooled clouds of Hydrogen compressed and the the great amount of gravitational compression created stars. Early stars were super massive. How stars are created were discussed in this IFOD: http://www.theifod.com/a-star-is-born/

Stars are atom smashing machines and burn via atomic fusion. Atomic fusion in stars cause hydrogen to gain protons and to change into the heavier elements – helium, lithium, carbon, oxygen, nitrogen, neon, iron etc.  Because early stars were super-massive they used their hydrogen fuel up relatively quickly (a few million years) and died.  When a super-massive star dies they explode via supernova.  These explosions scattered the heavy elements across the universe.  Supernovas continue to do this.

Life as we know it exists because of the carbon, oxygen, nitrogen, etc. that is found on Earth.  These elements came from the cores of the super massive stars that exploded billions of years ago. So, quite literally, we are all made of stardust.