The vast majority of the atoms currently present in the solar system, including those making up every human on Earth, were created billions of years ago: either at the beginning of the known Universe, or by processes that occur in stars. This means that every person is made of atoms that were forged by ancient cosmic events. 96% of human mass is composed of oxygen, carbon, hydrogen and nitrogen. Hydrogen, the lightest element, with atomic number 1 (meaning that it has only one proton in its nucleus) was created in the big bang, which scientists currently believe occurred almost 14 billion years ago. Hydrogen and helium atoms are combined by stars during the process of nuclear fusion to form other elements, such as carbon, nitrogen and oxygen. Heavier elements (such as gold, silver and lead) are created when extreme astrophysical events occur, such as supernovas.
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