Fossil preservation

The quality of a fossil depends upon the type of preservation that occurred during fossilization.

The remains of organisms may be fossilized in a variety of ways, including preservation of unaltered hard parts, chemical alteration of hard parts, imprints of hard parts in the sediment, markings in the sediment made by the activities of organisms, and the rare preservation of unaltered soft parts. Each of these types will be discussed below.

Some fossils are preserved in more than one way. For instance, an aragonitic coral may be replaced by silica, or recrystallized to calcite, but at the same time, it may also have its original pore spaces filled by permineralization. Similarly, a bone with original material also may have pore spaces filled by permineralization. As another example, fossil plants may be carbonized, but they may also leave external molds in the sediment.