Geologic Processes of Evolution

Science Links

Carbonization
Petrifaction
Replacement
Recrystallization
Soft-Tissue Preservation
Mummification
Organic Traps
Tar
Peat Moss


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Fossilization Process

Replacement

Replacement occurs when an organism is buried in mud and its remains are replaced by sulfide (pyrite) or phosphate (apatite) minerals. This process may replace soft tissue, preserving rarely seen details of the organism's anatomy. X-ray scanning of some German shales from the Devonian Period (410 million to 360 million years before present) have revealed limbs and antennae of trilobites (extinct ocean-dwelling arthropods) and tentacle arms of cephalopods (highly developed mollusks) that have been pyritised (replaced by pyrite). Paleontologists have used mild acids to etch the phosphatized fossil remains of ancient fish found in Brazil to reveal structures such as gills and muscles. Although mineral replacement is rare, fossils created in this way are important in helping paleontologists compare the anatomical details of prehistoric organisms with those of living organisms.