The other thing it’s important to notice about the top five elements of life is that only one, calcium, is truly and unambiguously a metal. Metals are important in living systems as trace elements, but the bulk of living systems is made up of nonmetals. And as we’ve already seen, that must mean that living matter is dominated by the covalent bond. This is why any vision of "crystalline" life is so alien—not impossible, mind you, just very, very weird. Covalent bonding works well for life. Unlike the ionic bonds that dominate in crystals, the covalent bond is not geometrically rigid—it can swivel. This means that biomolecules built on covalent bonds can be highly mobile and malleable. Furthermore, covalent bonds don’t dissolve like ionic bonds do. And covalent bonds store chemical energy, a feature that all living systems exploit. Much of the solar energy harvested by and channeled through the ecosphere is used to make substances full of energy-rich covalent bonds. There’s a word for such substances: food.

The elements of life combine in virtually endless ways to build the living matter I call Quantum Meat. But there are two covalent bonds which, I would argue, are more important than all the others. One of these we’ve already seen: the covalent bond between hydrogen and oxygen found in water. The other is the covalent bond between carbon and carbon.