What Are Little Boys (and Girls) Made Of?

Do you remember that little nursery rhyme? If not, here it is:

What are little boys made of?
Snips and snails,
And puppy dog tails,
That's what little boys are made of.

And its complement:

What are little girls made of?
Sugar and spice, and everything nice,
That's what little girls are made of.

I hate to be the one to tell you this, but, well, that's not exactly true. I'm going to tell you what we're all made of. Star dust. The remains of exploded stars. If you'll stick with me, I'll explain, and you will be enriched by the knowledge.

You see, first there was the Big Bang. About 13.7 billion years ago, the universe emerged "from a tremendously hot and dense state." In the beginning, there was only one element. Hydrogen, the lightest element, consisting of one proton and one electron. The hydrogen atoms eventually coalesced due to the force of gravity into stars. Stars, initially composed of hydrogen in plasma form, begin to burn when the temperature and pressure in the interior become great enough to set off nuclear fusion. The hydrogen is squeezed together, a nuclear reaction takes place, and Helium is created. Eventually, much of the hydrogen is burned up. When the star cools because its hydrogen fuel is running out, it's no longer able to balance the force of gravity trying to crush it, so it begins to collapse. At some point, the increase in density brings about a high enough temperature and pressure to begin a new fusion reaction, this time the fuel is Helium, and the result it the formation of Carbon and Oxygen. This cycle repeats itself, each time fusing the elements into even heavier elements. From Carbon and Oxygen comes Neon, Sodium, Magnesium, Sulphur, Silicon, Calcium, Iron, Nickel, Chromium, Copper. Eventually, if a star is massive enough, it will go all the way to supernova, and it's in this tremendous explosion that the rest of the heavier elements are formed, and the whole stew of elements is sprayed out into space. That's where we start to figure into it.

These heavier elements eventually formed planets like our earth, with its abundance of the stuff we are made of. By weight, we are 65% Oxygen, 18% Carbon, 10% Hydrogen, 3% Nitrogen, 1.5% Calcium, and small fractions of other heavy elements. None of these elements, except for hydrogen, would exist without stars and the process of nuclear fusion that takes place in their cores. If you'd like to learn more about this process, visit a very nice animation here.

P.S. A link to this article can be found on Cris Rowan's Philosphia Naturalis, a very nice blog carnival. Check out the carnival here.