4. The Elements of Life

Wow. We’ve covered a lot of ground. We’re in the home stretch now, but you need to bear with the old Quantum Butcher a while longer. After all, if you don’t eat your meat, you can’t have any pudding.

Now that we’ve surveyed the basics of chemistry (in about 6000 words—I think we’re all to be commended) we’re ready to talk about the elements of life. As I’ve already hinted, the elements of life are bound to have certain features—for one thing, they must be abundant. The ten most abundant elements in the universe, in descending order, are hydrogen, helium, oxygen, neon, nitrogen, carbon, silicon, magnesium, iron, and sulfur. Of these, seven are important in living systems—only helium and neon (non-reactive noble gases) and silicon are left out. The five most abundant elements in living systems are hydrogen, oxygen, carbon, nitrogen and calcium. Only calcium is out of the Cosmic Ten. But calcium is abundant in the earth’s crust, ranking eighth. The lesson for you sf writers out there is that it’s not a good idea to design your alien life forms out of large amounts of, say, chromium or lawrencium. Life is made of stuff that’s easy to get.