The comet had been captured eons ago by the the sun's gravity, and has been orbiting the sun ever since. On one orbit it passed near the earth, and a few spores locked in the ice of the comet's tail are captured by earths gravity and start to orbit the new planet. Millions of years pass as the spores are ever pulled deeper into the earth's gravity well, and eventually they start on a slow but steady decent to the surface. The spores alight in a field of exposed raw iron ore in what will eventually be northern Minnesota, and following their programming they move into the crystalline matrix of the iron, and start to multiply. They are alien evil incarnate, with endless patience. Eventually the planet's biped inhabitants take their giant earth movers and excavate the iron ore. Powerful machines crush the ore into powder, magnets separate the iron and roll it into small balls. The balls are sent to a foundry, and are melted into billets, with one of them still carrying the inorganic alien spores. The billet is sold to a manufacturer who makes stainless steel nuts. The spores are now embedded in thousand of stainless steel nuts, and their long wait is almost over. Destruction of all life on planet earth is their goal, and it is now within their reach.