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

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,