Fossilization Processes

A deceased organism typically begins to fossilize when it is buried before exterior deterioration takes place. The organism is covered in sand, or it may occasionally sink to the bottom of a swamp, lake, sea, or river. Upon burial, decomposition sets in and the body’s soft tissues are destroyed. The more durable parts develop into fossils. The organic remnants are safely stored and kept in good condition while water, sand, and mud solidify to rock.

Permineralization

The permineralization process is a type of fossilization that occurs when minerals carried by water fill in all the gaps in an organism or organic tissue. Mineral deposits create internal castings within these cavities. The organism must be covered by silt shortly after death for permineralization to occur; otherwise, scavengers or decomposition will consume the remains. When water transporting minerals from the earth, lakes, or oceans seep into the cells of organic tissue, a cast of crystals eventually forms. Permineralization is helpful while examining an organism’s internal systems, particularly in plants like the ancient Redwoods at Florissant Fossil Beds. Lahars or volcanic mudflows buried the ancient Redwoods in this area, which caused silica from the volcanic ash to largely precipitate inside the Redwoods’ cells.

Casts and molds

the original organism’s remnants fully vanish or are destroyed in some other way. External mold is the term for the residual organism-shaped hole in the rock. The resulting cast resembles the organism if the void is later filled with sediment. Endocast or internal mold occurs when the sediments fill an organism’s interior, such as the hollow of a skull or the interior of a bivalve or snail.

Authigenic mineralization

This is a unique method of creating molds and casts. If the chemistry is appropriate, the organism (or part of the organism) may function as a nucleus for the precipitation of minerals like siderite, leading to the formation of a nodule surrounding it. Very fine three-dimensional morphological information can be preserved if this occurs quickly before the organic tissue experiences severe degradation. 

Recrystallization

Recrystallization is a process through which the minerals that made up the original shell or bone of a fossil transform into a separate material made of the same chemical elements. Fossilized shells made of aragonite commonly recrystallize into calcite, a more stable variety of the same material. Recrystallization takes place when another mineral replaces the shell, bone, or other tissue. In exceptional cases, the original shell is gradually replaced by minerals at such tiny scales that microstructural features are preserved despite the total loss of the original material.

Adpression

Compression fossils, like those of fossil ferns, are produced when the intricate organic molecules that make up an organism’s tissues are chemically reduced. The fossil in this case is made of the original material, although this has undergone geochemical modification. This chemistry change is an indication of diagenesis. Compressions and impressions frequently take place in combination. For example, the phytoleim will frequently be attached to one part of the rock when it is broken open (compression), whereas the counterpart will only be an impression.

Soft tissue and molecular preservation

Cells and soft tissues should have decomposed after millions of years, and the preservation of cells and soft tissues after millions of years, in some dinosaur bones appears to be inconsistent. Cells and soft tissues within bone are often protected from total deterioration. A mineral concretion that forms around a bone protects the proteins inside from groundwater hydrolysis. A bone’s cells are protected from autolysis by iron infusion and coating during an important phase of the deterioration process. Collagen fibers in a bone are further protected by cross-linking and interaction with bone mineral surfaces. These protective elements have the potential to preserve soft tissue for millions of years.

Calcification and carbonization 

When an organism is carbonized or coalified, its remains are essentially converted to the chemical element carbon. A thin film that represents the original creature in a carbonized fossil is called a silhouette, and the original organic remains were typically soft tissues. Coal makes up the majority of coalified fossils, and the original organic material was mainly composed of wood.

Bioimmuration

Bioimmuration is generally defined as fossilization as a result of organic overgrowth which can preserve soft-bodied animals and soft sections of organisms with mineralized skeletons. Other creatures that are struggling for available living space frequently overgrow sessile species linked to hard or rigid substrates. On its underside, it may have a high fidelity (sub-micron size) impression of the overgrowing organism if it has a mineralized skeleton that is likely to become fossilized. The bioimmured organism may occasionally have a soft body and be retained in negative relief as a type of exterior mold. There are instances where a live, skeletal organism climbs upward as an organism settles on top of it, preserving the settler in its skeleton.

A fossil is a preserved remnant, impression, or trace of an animal or plant from a past geologic age by some natural process. Just a small proportion of extinct species have been preserved as fossils, and often only those with a solid skeleton are capable of being preserved. A calcareous skeleton or shell is found in a large number of major groups of invertebrate creatures (e.g., corals, mollusks, brachiopods, and bryozoans).  The organic tissues can be preserved in a shell or bone that is buried soon after deposition, they eventually get petrified (transformed into a stone substance). In sedimentary rocks, unaltered hard pieces, such as the shells of clams or brachiopods, are abundantly available.