The term for the preserved remains of ancient life is a fossil. Fossils include not only bones and shells, but also teeth, leaves, pollen, footprints, burrows, coprolites, and other traces left by organisms from the geological past.
Fossilization usually begins when an organism or its imprint is rapidly buried by sediment. Over time, minerals can replace or fill the original material, preserving its shape. In other cases, an impression hardens in rock, or a body is protected in amber, ice, or exceptionally dry conditions. Most organisms decay without leaving fossils, so the fossil record is necessarily incomplete.
The scientific study of fossils is paleontology. Fossils allow researchers to reconstruct extinct species, ancient environments, and the sequence of evolutionary change. Transitional fossils such as Tiktaalik, which combines fishlike and tetrapod-like features, have helped clarify major steps in the history of life.
An artifact is a human-made object, while sediment is deposited earth material and a mineral is a naturally occurring inorganic substance. Those terms may occur around fossils, but they do not mean preserved ancient life themselves.