Lecture 2 PDF

Lecture 2 Modes of organisms’ preservation: 1- Preservation without alteration: In rare instances no alteration can take place and the original parts, including soft body tissue, can be preserved intact. This occurs most often in cold or arid climates where an organism can be frozen i...

Lecture 2 Modes of organisms’ preservation: 1- Preservation without alteration: In rare instances no alteration can take place and the original parts, including soft body tissue, can be preserved intact. This occurs most often in cold or arid climates where an organism can be frozen in ice or desiccated in dry desert air. Desiccation is the process by which all water is removed from the organism. Examples of these processes include frozen mammoths that have been retrieved from ice in Siberia and early Egyptian remains that have been dried in the dry desert sands. 2-Preservation with alteration: Most fossils have been altered in some way from their original form. Some of the more common alterations that occur in fossils are permineralization, replacement, carbonization, recrystallization, and the production of molds and casts  Fossilization processes 1-Permineralization: is a process of fossilization that occurs when an organism is buried the empty spaces within an organism (spaces filled with liquid or gas during life) become filled with mineral-rich groundwater. Minerals precipitate from the groundwater, occupying the empty spaces. This process can occur in very small spaces, such as within the cell wall of a plant cell. Small scale permineralization can produce very detailed fossils. For permineralization to occur, the organism must become covered by sediment soon after death or soon after the initial decay process. The degree to which the remains are decayed when covered determines the later details of the fossil. Some fossils consist only of skeletal remains or teeth; other fossils contain traces of skin, feathers or even soft tissues. 2-Carbonization: is the complete change through chemical processes of the original plant or animal remains to a thin layer of carbon that outlines the original body shape. In some cases this process allowed the preservation of details in soft body tissue. 3-Recrystallization: is the process by which less stable forms of a mineral structure convert into more stable forms. This is most often seen in the shells of clams and snails. These shells are typically made of a form of calcium carbonate known as aragonite; over time the aragonite structure will slowly turn into the more stable calcite. 4-Freezing: It is a type of preservation in which the organism frozen. Such ideal remains are rare and almost always never very old. Like the hairy mammoth. These remains have preserved bone, skin, muscle, hair and even internal organs. 5-Drying or Dessication Remains of animals that have been found thoroughly dried include camel, ground sloth and even marsupial wolf. These remains were found in caves in arid and semi-arid areas of the Southwestern United States, South America, New Zealand and Australia. The dried dung of cave dwelling giant ground sloths have also been found in caves. 6-Petrification Petrification is a geology term denoting the processes by which organic material is converted into stone or a similar substance. It is approximately synonymous with fossilization. Petrified wood is the most well known result of this process. 7-the formation of molds and casts: Many of the fossils that you will observe in the field are actually the mold or cast of the organism. A mold: is formed when the hard body material of the buried organism is removed by dissolution. The print that is left behind will then retain the shape of previously existing body. This is similar to making a handprint in freshly poured concrete. Molds can express the external structure of the object. A cast : is formed when the initial object has dissolved, the mold becomes filled with sediment or mineral deposits, the original shape of the object can be regained in the form of a cast.