Answer: Fossil
Fossils are the remains or traces of dead living beings. Fossils are formed when the soft parts of the dead organisms gets decomposed by the action of microbes present in the soil and only hard skeleton is left like stem or bark in plants and bones in animals and humans. These remaining parts are buried under different layers of soil strata. The soil containing dead remains gets compacted in the form of hard rock.
The material formed by bits of rocks and bits of once-living parts of plant is called fossil.