Usually occurring in layers of sedimentary rock distributed around the world, a fossil is any geological imprint of a once-living life form and the study of fossils is known as paleontology.
Fossils can be found by deliberate searching but they are often discovered as a result of industrial mining, development, natural disasters or weathering. A specimen need not die to leave a fossil, but the best fossils occur when a specimen is buried alive or rapidly after death as in land-slides, tar-pits, volcanic catastrophe and river-bank sediments. This process can occur in land, water or even amber, a hardened form of tree sap, often resulting in unaltered preservation. Water-dwelling creatures comprise the most common fossils, and natural mineral growths are occasionally mistaken as fossilized organisms.