There are many processes that lead to fossilization, including permineralization, casts and molds, authigenic mineralization, replacement and recrystallization, adpression, carbonization, and bioimmuration.
to dinosaurs and trees, many meters long and weighing many tons.
The remaining organism-shaped hole in the rock is called an external mold.
If this hole is later filled with other minerals, it is a cast.
Nodules from the Carboniferous Mazon Creek fossil beds of Illinois, USA, are among the best documented examples of such mineralization.
Replacement occurs when the shell, bone or other tissue is replaced with another mineral.
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.
Fossils may also consist of the marks left behind by the organism while it was alive, such as animal tracks or feces (coprolites).These types of fossil are called trace fossils or ichnofossils, as opposed to body fossils.Some fossils are biochemical and are called chemofossils or biosignatures.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. In some cases the original remains of the organism completely dissolve or are otherwise destroyed.An endocast or internal mold is formed when sediments or minerals fill the internal cavity of an organism, such as the inside of a bivalve or snail or the hollow of a skull. If the chemistry is right, the organism (or fragment of organism) can act as a nucleus for the precipitation of minerals such as siderite, resulting in a nodule forming around it.If this happens rapidly before significant decay to the organic tissue, very fine three-dimensional morphological detail can be preserved.Paleontology is the study of fossils: their age, method of formation, and evolutionary significance.Specimens are usually considered to be fossils if they are over 10,000 years old. This is an informational tour in which students gain a basic understanding of geologic time, the evidence for events in Earth’s history, relative and absolute dating techniques, and the significance of the Geologic Time Scale.is any preserved remains, impression, or trace of any once-living thing from a past geological age.