martes, 25 de mayo de 2010

FOSSILS



Fossils (from Latin fossile, which is extracted from the earth) are the remains or signs of activity past organisms. These remains, preserved in sedimentary rocks may have undergone changes in its composition (diagenesis) or deformation (dynamic metamorphism) more or less intense. The science that deals with the study of fossils is Paleontology.

The best-known fossils are the remains of skeletons, shells and animal carcasses, and carbonaceous impressions of plants. However, fossils are not just those from the hard parts petrified of these creatures are also considered as fossils, the remains unaltered molds, bioconstructions, or traces of the activity they have had on different substrates or organic sedimentary (dwelling, resting, feeding, predation, etc.).. In an extreme case, oil, hydrocarbon fluid composed of organic origin, must be considered both a "rock" as a fossil sedimentary chemical.

The oldest fossils are the stromatolites consisting of rock created by the deposition of substances such as calcium carbonate, through bacterial activity. [4] The latter has been told by the study of stromatolites current produced by microbial mats. Gunflint Formation contains abundant microfossils widely accepted as microbial residues. [5] There are many kinds of fossils. The most common are remains of shells or bones turned to stone. Many of them show all of the features of the shell or bone, even microscopically examined. The pores and other small spaces in their structure are filled with minerals. Minerals are chemical compounds, such as calcite (calcium carbonate), which were dissolved in water. Going through the sand or mud snails containing the bones and the minerals were deposited in the spaces of their structure. That is why fossils are so heavy. Other fossils may have lost all the marks of its original structure. For example, a snail originally of calcite can be dissolved 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 left the hole in the stone, a kind of mold that can be filled with plaster paleontologists to discover how they saw the animal.

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