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A fossil is the remainder (shell, bone, tooth, seed, sheets…) or simple moulding of an animal or a plant preserved in a sedimentary rock. The fossils and the processes of fossilization are studied mainly within the framework of the Paléontologie.

According to the species and the periods, the fossils can be various qualities and more or less abundant. The process of fossilization is exceptional, and testimonys which the fossils bring to us on more than three billion years evolution the life on Ground are still lacunar and will certainly remain it.

Historical elements

The fossils, as material elements, are known of the Man since very old ages. Aristote, for example, refers to fossilized elements. However, the two essential ideas about them, i.e. their origin organic and the fact that they are testimonys that other forms of life existed before the Man, were not truly apprehended before the 17th century.

The first real progress rises from a proposal clarified at the beginning of the 18th century: the grounds containing of the fossils of animals or marine plants were in all logic to be covered by the sea, so that they settle on the bottom and are inserted there on the bed Sédiment surface. It is the first time that the fossil is considered like stratigraphic index . However, the intellectual weight of the idea of spontaneous Generation, according to which the species had appeared the ones after the others and of divine origin, prevented a systematized and thorough interpretation of the causes of the renewal of the species, such as logically deduced from the study of the fossils.

Following this first progress, the idea of a filiation enters the species made its way, in particular in the writings of Geoffroy Saint-Hilaire and Lamarck. Are opposed then the visions creationnist, creationist on the one hand, transformist, evolutionary on the other hand. The heart of the controversy is reached when with the question of the origins of life animal and vegetable that is mixed with the origins of the Man.

It is also at the 18th century that three large branches divide the Paléontologie - and remain still to date, in the form of disciplinary specialities: descriptive and comparative paleontology, of Vat; evolutionary paleontology, of Lamarck; a little later, stratigraphic paleontology, of Oppel and Orbigny. The Paléogéographie follows about 1830.

In a very clear way, paleontology and fossil were opposed de facto to a dogmatic Église , same manner as the Astronomie with the Moyen-âge. Multidisciplinary, organized like a historical investigation, the study of the fossils also had important implications on the report/ratio of the Man to the Temps, for example on the question of the age of the Earth or alive, or on the question of the durations - the basic temporal unit of a fossil is the Million years, a not easily conceivable amount of time. Thanks to fast and important progress in the techniques of observation and investigation, the knowledge of the fossils and fossilization during the geological Temps carried out its larger projections as from the 19th century.

The last fossil to have been discovered is that of the Lognkosauria, fossil discovered in 2007, its skeleton was to 70% and is 3rd the larger ever discovered in the world and also most complete of them.

Fossilization

The Fossilisation of the living beings is in general a process of Minéral isation (replacement of living tissue by mineral substances) in Sedimentary rock which is the rock par excellence for the conservation of fossils. In rather rare cases, one can have a conservation of the organic matter (Mammouth in the Pergélisol, momification in Bitume, inclusion in Ambre). In other cases, in fact only traces of biological activity are preserved (Paléoichnologie).

An example: the petrified forest

The thousands of fossilized trunks of the National park of Petrified Forest (Arizona) date from the Trias (approximately 200 million years). The area was then occupied by the delta of a river on the banks of which pushed giant trees. After their death, they were hidden under deposits Sédiment surfaces rich in Silice, which supported the conservation of their structure. Silica replaced the vegetable matter slowly and fossilized the trunks. Gradually, the area was inserted and was buried under sedimentary layers. Its recent rising, combined with the erosion allowed the setting the day of the fossilized trunks.

Use

From time immemorial, the fossils intrigued the men who, according to the times, gave them various significances: talismans, remainders of giants, objects malefic, animal disappeared at the time of the flood. It is only at the 19th century, with work of Charles Lyell, Jean-Baptiste de Lamarck then of Charles Darwin and the theories of the evolution, then of the theory of the Plate tectonics , formulated by Alfred Wegener in 1915, that is set up the modern theoretical framework in which are studied the fossils.

For the general public, the fossils are especially known thanks to some characteristic families like the Ammonite S, kinds of Céphalopode S sailors, the Trilobite S of the family of the Arthropode S, the sea urchin S… or finally the fossil plants preserved in the coal (Fougère S, Prêle S…). The stars of Saint-Vincent are examples of fossils used like jewels.

Lagerstätten

Certain fossiliferous sites of an exceptional quality as the lithographic Calcaire of Solnhofen in Bavaria bear the name of Lagerstätten. This one holds for example one of the splendid examples of Archéoptéryx . These fossiliferous layers are so rare that with each one of their discovery or redécouverte, they upset the vision of the progression of the life.

See too

stratigraphic Microfossile
Fossil
Fossil alive

External bonds

Paleontology:: Parisian Eocene - miocene of south-west
Fossil of the south of France
paleontology and the fossils
paleontology, fish fossil and layers of Fossil Provence
the Vertebrate ones and large layers paleontological
Site dedicated to the study of a layer in Paris region
Gate on Paleontology
Blog of one impassioned of fossils and Paleontology
PP Collections, Dominican Amber and inclusions , amber Collections

Simple: Fossil Sale of fossils to the biddings at Christie' S in 2007. Text and photo Catherine-Alice Palagret.

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