Everything is made up of atoms made inside stars.

Small planets like ours don't have enough gravity to hold on to much hydrogen or helium gas since both of those are very light.So, even though carbon, nitrogen, oxygen and so on made up only two percent of the gas cloud from which Earth was formed,these heavier elements form the bulk of our planet and everything on it.Think about this:with the exception of hydrogen and some helium,the ground you walk on,the air you breath, you,everything is made of atoms that were created inside stars.When scientists first worked this out over the first half of the 20th Century,the famous astronomer Harlow Shapley commented,"We are brothers of the boulders, cousins of the clouds."