A fossil is the remains of an ancient life form—plant or animal—or its traces, such as nesting grounds, footprints, worm trails, or the impressions left by leaves, preserved in rock. Fossil traces are called ichnofossils. Fossilization refers to the series of postmortem changes that lead to replacement of minerals in the original hard parts (shell, skeleton, teeth, horn, scale) with different minerals, a process known as remineralization. Infrequently, soft parts may also be mineralized and preserved as fossils. A new category of subfossil—a fossil that has not yet begun to mineralize—is increasingly recognized in the scientific literature. Many subfossils originated in the Holocene or Recent, the period that we now live in, and cannot be dated with any greater accuracy. In addition, the term "fossil" is applied in other ways, for example, to preserved soils and landscapes such as fossil...