Fossils (from Latin 'Fossil', and means: 'which is extracted from the earth'), are the remains or signs of past activity of organisms. These remains, preserved in sedimentary rocks may have undergone changes in its composition (by diagenesis) and deformation (by dynamic metamorphism) more or less intense.

The science that deals with the study of fossils is Paleontology.

The most well known fossils are the remains of skeletons, shells and carapaces of animals, and plants carbonaceous impressions. However, the fossils are not only those from the petrified hard parts of these creatures. are also considered as their fossil, remains unaltered, molds, bioconstructions, or traces of activity that printed tracks in different sediment or organic substrates, (dwelling, resting, feeding, predation, etc.)

 

Etymology and evolution of the term

The word fossil is derived from the Latin verb 'fodere', dig, through the 'fossil' substantive, 'that is excavated'. Throughout history, and earlier, in prehistoric times, man has found fossils, remains of living creatures petrified by the minerals that the body was in contact. These minerals that were replaced or preserved their external form. Primitive man gave them a magical significance. And the authors of classical antiquity had observed, and generally interpreted correctly. The term fossil is employed as 'Plinio' in the first century and its use was recovered in the sixteenth century by 'Agricola', referring to their body buried (as derived from fossa) and involved the body as organic minerals embedded in the materials of the earth's crust. This situation continued until early last century, if indeed the real fossils were distinguished as organized fossils. British geologist Lyell described the fossils as remains of organisms that lived in the past and which are integrated within the sedimentary rocks. This definition is valid, but now generally given to a broader term, and which are in the same manifestations of the organisms activities like excrement (coprolites) and organic remains of buildings, footprints, impressions of body parts, skeletons or round logs, etc..

 

Fossil Types

The oldest known fossils are stromatolites, which consist of rocks created by the deposition of substances such as calcium carbonate, due to bacterial activity. The latter has learned through the study of stromatolites current produced by microbial mats. Gunflint Formation contains abundant microfossils widely accepted as microbial remains. There are many kinds of fossils. The most common are the remains of processed snails in stone or bone. Many of them show all the details of the original bone or shell, even microscopically examined. The pores and other spaces in their structure have been filled with minerals. Minerals are chemical compounds, such as calcite (calcium carbonate) were dissolved in water. Contact with the sand or mud in which were contained snails or bone caused these minerals were deposited in the spaces of the structure. That is why fossils are so heavy. Other fossils, however, may have lost all the marks of their primitive structure. For example, a shell originally calcite may dissolve completely after being buried. The impression left in the rock can be filled with another material to form an exact replica of the snail. In other cases, the shell is dissolved and only remaining hole in the stone, a kind of mold that can be filled with plaster to discover how the animal would be.

The fossils are usually only hard parts of animal or plant: the trunk of a tree, the shell of a snail or the bones of a dinosaur or a fish. Some fossils are more complete. If a plant or animal is buried in a special kind of mud that contains no oxygen, some of the soft parts also can be preserved as fossils.
The most spectacular of these "perfect fossils' are complete woolly mammoths found frozen in the soil. The meat was so perfectly preserved in ice, which could be eaten even after 20,000 years. Conventionally estimated as the most recent fossil remains of organisms that lived at the end of the last Quaternary glaciation (Würm), ie about 13,000 years ago. The remains beyond (Neolithic Age of Metal, etc..) Are commonly regarded as 'subfossils'.