If dust is taken to mean soil, with all of its microorganisms and built-up matter from the life and death of plants and animals, then yes, the argument can be made that people are made of dust (at least indirectly, although I'm guessing that but the most disgustingly clean people consume at least some dirt in their lives--it's really hard not to). When you look at the food chain, you see that plants grow in the soil--dust, if you will, and some do grow literally grow well in dry, dusty conditions--animals eat the plants, other animals eat those animals, all the organisms shed wastes and leave dead or dying cellular material on the ground, each other, the atmosphere, which are consumed by microorganisms (not to mention that multicellular organisms typically have large quantities of microorganisms living on them, and in fact the microorganisms and multicellular organisms need each other to survive), then it can be argued that all life is made of "dust" and eventually returns to "dust" and is reused in the life cycle. Humans, of course, in spite of fundies insistence that we are somehow special and outside this cycle, are no different. Being omnivores, we eat both plants and animals (and fungi, for those of us who like mushrooms), and of course consume microorganisms while we're at it. Throughout the course of a lifetime, no matter how long or short that life may be, we produce wastes, shed dead hair and skin, and eventually, when we die, our bodies (usually) are reabsorbed by the environment (even embalming doesn't stop this, but only delays it; cremation just breaks us down to our basic elements, and when those ashes find their way back into the air and soil, they are quickly absorbed back into the environment). Some people and animals, for various reasons, some natural and some manmade, become mummified, but this only delays the process (by a long time by human standards, to be sure, but nevertheless, everything will eventually return to nature). Granted, under the right circumstances mummified may become fossilized, and bones and teeth, due to their hardness and mineral content, are fossilized often enough to make observations about the distant past possible (and no, those fossils were not placed there by God to test us, they were placed there by chance and circumstances that allowed preservation). Even fossils, though (and fossil fuels like coal and oil) are a part of the environment (and coal definitely produces dust), and given the right circumstances and chemical changes, find their way back into the life cycle.
So, yes, the argument can be made that life is of dust and returns to dust (again and again and again).
