It is sometimes unbelievable, when I think to myself that these 118 elements are all we have. You cannot find anything in the universe that is made of stuff that is not in our periodic table. The Hydrogen in our bodies is the same as the Hydrogen inside our sun.
We all know about the big bang. During the first three minutes after the big bang only several atoms were formed. Hydrogen, Helium and little bit of Lithium. Nuclear reactions need very high temperature, apparently, when the universe was expending it was cooling quickly at the same time. Consequently, the fission reactions stopped and these three elements were the only ones in the universe shortly after the big bang.
So, where do the other elements come from? “The fault in our stars”. The newly formed stars are mostly made of Hydrogen gas. The nuclear reactions that take part in the core of the stars make possible the “birth” of new elements. Helium, Carbon, Nitrogen and so on. The variety of the elements depends on the mass of the star. For example, our sun is very little, thus it can only create Helium atoms inside it. When all Sun’s Hydrogen converts into the Helium, it won’t have enough temperature inside it to generate other nuclear reactions, since pushing two helium atoms require a lot more energy. As a result, some day our sun will become a red giant, because outer layers will eventually get puffed out.
The creation of heavier elements is not possible without big stars. They can generate more complex nuclear reactions and all the elements till Iron. The Iron is the point when star gets into trouble. The iron atom is so stable, it is energetically inefficient for the stars to keep on nuclear reactions. Gradually, star wastes all the Silicon and the created Iron stops all the reactions that kept star alive. The center of the star begins to shrink and it finally collapses, creating a Supernova.
So, what other heavier elements come from? After the big star collapses, the center, which was made of Iron, shrinks and is pushed together. The temperature rises and thereby this titanic explosion gives birth to other heavier elements.
The universe has only several seconds to create elements after Iron. That is why we have so little gold or mercury. The elements in our body were created by dead stars. After several massive explosions they found themselves in the outer layer of our planet. Even the Voyager 1 was made of the atoms which “came” to earth from far away. And now “these atoms together” are exploring the deep space.
We do not own our atoms, we borrowed them from the universe and we are constantly exchanging. None of the atoms we were born with are with us now. And what I find the most exciting is that, most of the atoms in our body are very, very old. Some of them even 13.7 billion years old.
Our bodies consume the most abundant elements in the universe, but we also need some trace elements. E.g. 75 mg of copper, that is exactly 7.0546875 * 1023 atoms, which were formed during the collision of a big star. If we don’t have these 7.0546875 x 10^23 atoms in our body (approximately, of course.), we may develop some coronary heart diseases.
To conclude, we are made of a stardust and we need the tiniest pieces of the universe to survive. This picture below is one of my favorite and I think it clearly illustrates and summarizes my view.