Fossils are usually categorized in two different ways, unaltered or altered. An example of an unaltered fossil are shells buried in the mud of the sea floor or even whole carcasses of large mammals from the Ice Age that have been found frozen and preserved in ice for as long as twenty five thousand years. Another example are insects like mosquitoes, that have been preserved by being encased in amber. Altered fossils are fossils that have been preserved as the result of alteration of the buried organism, usually its hard parts. These alterations can take place under six forms. Replacement fossilization is when part of the original material has been dissolved and some other substance has taken its place. The fossilization process when mineral substances are introduced to the pores of porous materials such as bones and

shells is called permineralization. In distillation, The soft parts of organisms, containing nitrogen, oxygen, and hydrogen, are removed during the fossilization process. Another example of altered fossils are molds and casts. This process of fossilization is achieved when a hard part of an organism leaves an impression in soft mud and is later removed, leaving the impression to be preserved in the mold. Animals can also leave footprints and tracks in mud that is then hardened to form a rock. After examining one fossil, it may be decided that it was an altered fossil that had been found. It was a stropheodonta brachiopod, and it had undergone permineralization fossilization. It is believed the earth was formed about four and a half billion years ago. A time scale has been developed by scientist, which divides geological time into periods based on climatic and geological changes.

Fossils are amazing how they are formed. The process is fossilization. A series of mistakes must happen in order for a fossil to be created. In order for fossils to form, there must be a way to preserve the dead remains of animals and plants for a time so that they do not decay completely. Some living creatures must die and must some how escape the scavengers that have a roll in the food chain. The most common way that this occurs is on the bottom of bodies of water. When an animal of plant dies and falls into the water, the remains are sometimes covered up quickly by sediments. The layers of sediment form a protective covering to slow the process of decay. Over thousands of years, the sediments around the remains harden into rock. The dead animal or plant remains eventually decay leaving an empty space inside the

Some topics in this essay:
Ice Age, , Maxilla Amandidle, School Medicine, Glacier Peak, Tamie Talan, animal plant, fossils preserved, process fossilization, harden rock, study fossils, glacier peak, empty space, preserved ice, altered fossils, minerals filter,