How are fossils formed? There are many processes by which plants and animals or their impressions can be preserved. Most living things after death decay or are eaten by scavengers. Teeth and bones which are very hard last much longer. The word fossil is used to refer to more than one type of plant or animal remains. First there are the actual remains of the plant or animal that can be preserved. An insect enclosed in amber is an example. The actual biological material still remains encased inside the amber. Next there is the case where a structure of the animal may be preserved but the actual tissues and bones have been replaced by new material. An example would be fossil trees in Arizona. The wood has been replaced by silica. The rings and structure however are still present. The next type fossil type is where the shape has been preserved but the material is gone. An example of this is a fossil footprint (called ichnite). The animal steps in soft limy mud that sets up quickly like concrete so to speak which then hardens to rock. This leaves the impression of the object so size, shape and aspect ratio can be measured. An example would be a footprint of a dinosaur or of a man.
The processes where fossils can be formed can happen in different ways.
- FREEZING: The best example of this is in Siberia where thousands of mammoths have been found frozen. Their flesh and skin are still present. The meat has been thawed and eaten for centuries. What catastrophe caused thousands of animals to be frozen across vast areas of the continent is up for debate. Many theories abound. Many frozen mammals have also been discovered in Alaska as well.
- DESICATION: We probably have all seen examples of dried out mice or flies found in the desert or perhaps in your hot attic. All it takes is a hot dry environment and the right conditions and the life form dries out and its parts are still there minus the water that evaporated from the object. Maybe you have found an old lemon in your refrigerator that dried out and is as hard as a rock.
ENTOMBMENT: Common examples are insects encased in amber. An insect lands on some tree sap and struggles to escape.
It is stuck and it dies while more sap from the tree engulfs its body. The tree dies and must experience some catastrophe
where it is buried under water or earth. If it were not covered it would decay and the amber would decay. Microbes
would destroy both. But if buried and preserved from scavengers and bacteria it would survive. The tree sap hardens over
the years and amber results. No one is sure how long this takes because no one seems to be performing experiments to find out.
Lots of amber is found in and around the Baltic seacoast. It is assumed that the salt water undercuts the strata at the bottom of the
sea and the lighter amber floats to the surface, washes ashore and is found along the beaches.
Another good example is the La Brea tar pits in los Angeles; mammals, birds, and insects found there have mostly bones preserved. Carbon 14 dating shows ages in thousands of years (saber tooth tigers, Smilodon 12,000 to 28,000 C-14 years). In this case all of the skin and tissue are gone. Bones, shells, teeth and some hard nut casings are found. One interesting theory is that a watery catastrophe (s) drowned the animal life and moved the disarticulated bones into a depression where an earthquake later released the underground tar to engulf and preserve the bones and their collagen content. Evidence for several theories will be discussed in a future article. Similar collections of bones are found in Peru and France as well.
- PERMINERALIZATION: This typically is what most people think of as a fossil. In their hand they hold a piece of petrified tree that is now made of stone. The woody material was replaced by silicon material over time. It was thought that the process took millions of years. Recently scientists have shown that woody materials can be rapidly turned into stone. All it takes is the wood to be immersed in hot silicon rich water for a few years.  Such conditions can be found in the Yellowstone hot springs as an example. As with any chemical reaction the temperature of the fluid and the concentration of the minerals would determine how much it took. Fossils have also been created by paraffin deposits and volcanic ash (Pompeii, Italy).
- CARBONIZATION: This process appears to be what causes coal seams to form. For hundreds of years scientists thought that coal took millions of years to form using heat and pressure. Now scientists know better. Under the right conditions coal can be formed in a matter of months. Oil also can be formed in a matter of months under the right conditions. Soft organic material may be preserved by carbonization or distillation where nitrogen, oxygen, and hydrogen are lost and a carbon replica of the organism is produced. Jellyfish and parts of trees have been preserved this way. These fossils are usually found in black shale that deposited under oxygen free conditions. X-Rays of black shale have revealed carbonized films of the soft parts of organisms which would not otherwise be visible (4).
- IMPRESSIONS: This process would involve a plant or animal being encased in some rock like material that hardens with time. Such events could be from volcanic lava flows, pyroclastic flows, fumoroles, etc. When the material hardens it takes the shape of the plant or animal inside. Possibly while it is hardening the material inside is decomposing or burning. The end result is only an impression of the object and a small amount of carbon sometimes left inside. Many scientists report that fossils often have a layer of carbonized material on them.
- The picture at the top was taken in the Morrison formation in Colorado from a recent road cut. It exposed a buried petrified log and branches. The curious thing was the center mineralized material was surrounded by a 1/4 inch thick layer of carbon in the form of a low grade coal. The carbon was tightly bonded to the mineralized material. What happened? Did the tree bark turn to coal under heat and pressure while the woody material absorbed hot mineral soaked water? It is quite common for mineralized fossils to have a layer of carbon on them. Do you have some knowledge of the subject you would like to share?  Email us.
- A careful examination of the picture will show that the dark black to the bottom and left is carbon and not a shadow of the mineralized material as some suggested after seeing the picture. We also have other photographic views as evidence.
- Whenever available our Paleo Group collects this carbon and has it carbon dated. Surprising to many people is that this carbon always turns out to be dateable implying that the carbon and the organism from which the carbon came is thousands not millions of years old!
- Earth History and Plate Tectonics an introduction to historical geology by Carl Seylert and Leslie Sirkin 1973 Lcc card number 72-8262