In biology, living things are placed into five kingdoms which branch and narrow until a single species is reached. This system of categorization places organisms with genetic similarities closer to one another — a way to track and sort changes in evolution. Minerals, on the other hand, are classified on the basis of their chemical composition. Both of these methods of classification lie on the basis of relative certainty. Neither DNA nor chemical composition can easily be modified — things exist as the things they are because they cannot physically be anything else. There is a limit to everything. - A piece of Fool’s Gold, next to worthless, existing as an emulation of the international standard for currency. - A barnacle, biologically sessile, even in death, waiting in place day after day for the crashing waves. - A deposit of salt, dried out in an old lake bed, left behind by the ocean it was once a part of.