The process of fossilization is not an easy one and there are several different ways that this process takes place. Some of these methods that form fossils are extremely rare. A fossil can be as large as the dinosaurs that once roamed our planet or as small as a micro organism but the process are the same. These include freezing, drying, asphalt, amber, carbonization and permineralization. To understand how each of these work we need to look a little deeper into how fossils are formed.
Millions of fossils have been found all you have to do is look into some of the museums that dot our cities. University paleontologist labs and fossil dealers hold many specimens, not including private collectors but even with all of these; it only comes to a fraction of the life that inhabited out earth throughout time.
The first step of fossil formation is that something must die such as plant, insect or animal to accomplish this. It must die near water or fall in water shortly after its demise. The water acts as insulation against any elements that would otherwise contribute to its decomposition. For example if a trilobite dies of old age at sea bottom, bacteria takes care of the soft parts of the body but leaves the exoskeleton intact. Soon sediments cover up the skeleton that remains. This has to happen rapidly in order to achieve fossilization.
There are other effects that can help to fossilize, such as landslides and mud slides. River deltas are also great for quick accumulation of sediment. If a trilobite dies and is covered in any of these, the fossil formation is started. Sediment has a very big influence on how well the fossil will turn out, if the sediment is fine and grainy something like clay, it allows for more detail but course sediment like sand shows less. The chemical of the sediment also has an influence on the fossil, for example, if there is a lot of iron in it, the rock will be red while phosphates will darken the rock to gray or black. So much depends on nature while the fossil is being created.
As time passes sediment will keep piling on the fossil and will compact the layers under it due to the sheer weight, this is what eventually, turns the sediment to rock. If it happens that water can seep down through the rock to reach the fossil it would be even better. Some of the minerals stick to the sediment forming a sort of glue to hold everything together. Ultimately after millions of years the trilobite is totally dissolved leaving a perfect imprint in the rock it laid on.
There is something else that happens after millions of years. The continental plates shift banging into one another, what was sea floor becomes dry land this all adds to bring a fossil to the surface and eventually it will be discovered. When a fossil comes close to the surface wind, rain, freeze, thaw and earthquakes all help to reveal it. That is the wonder of nature. There are different methods to form fossils.
Freezing
Freezing is the best method of fossilization but it is so rarely found that when it is, it is big news. In this method the animal must have been frozen in ice from the time of its death to the time of discovery which limits the possibilities of finding such a fossil. But this does happen and a good example of this was the mammoth and wooly rhinoceros found buried in the ice in Alaska and Siberia. This was exciting finds as the ice had perfectly preserved the whole animal with flesh, skin and hair attached. Some fossils that have been found frozen suggest they were flash frozen as there was food found in the mouth as well as the stomach. This tells scientist that the process of freezing happened very quickly.
Drying
This process is what scientists find in mummification. This applies to humans as well as animals and both have been found with this method. These fossils are usually found in very dry, arid parts of the world. If the fossil is completely dry it is possible that it will still have soft tissue with skin and organs. The fossil can be fossilized for thousands of years in this manner and have been found in the same form but this method totally depends on how dry the climate is.
Asphalt
You may think that this is an odd way to find a fossil but the La Brea Tar Pits or better known as the Hancock Park in downtown Los Angeles hold approximately 100 pits that have tar or sticky asphalt. These pits were formed by crude seeping from fissures deep in the earth. When this asphalt rises to the top the oil that it holds evaporates and leaves the sticky asphalt substance.
In these pits there have been numerous and high quality fossils found. These fossils are estimated to be 10 to 40 thousand years old which proves that asphalt to be an excellent preservative. There have been many findings in these pits such as bones, teeth, shells, the exoskeleton of insects and even some plants and seeds.
Amber
When an insect is found in amber, there is a process that happened to the insect many centuries ago. Imagine a fly getting trapped in tree resin, the more it struggles to escape the deeper into the resin it goes until it is fully encased. The tree eventually falls into a river or swamp. It takes millions of years but eventually this tree becomes a coal deposit. The resin that has the fly inside, by now, is hardened into amber. As the years pass the water recedes and uncovers the coal bed and when the erosion reaches the amber it floats to the surface due to amber being lighter than salty water. This process takes more time than we can imagine and when it is found on some shore you can be sure it is a message from the very distant pass. This is usually how insects and plant fossils are found.
Carbonization
This process of making fossils belongs to such things as plant leaves, soft body parts of fish, reptiles and marine invertebrates. These decompose only leaving the carbon behind. This carbon can create an impression in rock that will outline the whole fossil specimen. This can happen with such detail it is amazing how accurate some fossils can be.
Permineralization
Of all the ways fossils are formed this is the most common method of preservation. The cellular spaces that are left with the fossil fill with minerals and crystallize. The fossil is created in rock and outlines the exact shape of leaf or plant that was fossilized. Usually the material of what was there just melts away leaving behind a perfect picture.
Summary
Fossils are messages that have been sent to us from millions of years ago, in some cases. They are a process that has taken a very long time to finish. They have given us a glimpse into what use to be. Per mineralization seems to be the most common type of fossilization but there are others such as peat bog which is found in Ireland, paraffin deposits and especially volcanic ash like the ash that was found in the digs of the Cretaceous period with the extinction of the dinosaurs. It may not be finished yet as scientist strive towards finding out more and more about fossils. It makes for an exciting future.
