A decomposition does not end after the soft tissue has disappeared. The skeleton also has a decompositional rate that is based on the loss of organic (collagen) and inorganic components. Some of the inorganic compounds we use to determine the length of time since death include calcium, potassium and magnesium. (ibid)
In a temperate climate for example, it normally takes ten to twelve years to decompose fully to a skeleton. Therefore, the high number of variables involved making exact calculations based on a few characteristics of decomposition are extremely difficult and very often all the possible decomposition factors have to be taken into account.
The role played by microbes and bacteria is extremely significant in the decomposition process, but difficult to use as a dependable measurement in forensics as there are a vast amount of different types of bacteria associated with the decomposition of the body. These include Staphylococcus, Candida, Malasseria, Bacillus and Streptococcus spp. As well as putrefactive bacteria anaerobes. (ibid)
As an experienced researcher in this area states, "... every micro-organism known is involved in some aspect of the human decomposition cycle from Acetobacter to Zooglea." (ibid) Bacteria can also increase the body temperature after death." In some rare cases, the body temperature has actually increased after death before it cools down. Pathologists accredit this phenomenon partly to bacterial growth that goes unchecked after death." (McLemore, J. 1993)
Both bacteria and insects play an important role in the initial stages of decomposition. A good example of this was the exhumation of a soldier buried during the Civil War in the United States. When the coffin was opened it was found that the corpse was relatively fresh. This was due to the fact that, "at the time prominent solders were buried in solid lead coffins - the lead had 'sterilized' the body by poisoning the microflora and decomposition had not progressed past initial autolysis. (ibid)
Another factor that can radically affect decomposition and decomposition rates of the human body is moisture and water which will usually increase the rate of decomposition by as much as four times that of decomposition of a body on dry ground. "Immerse the body in water and skeletonization occurs approximately four times faster; expose it to air, and it occurs eight times faster." (Decomposition: Wikipedia) central factor is that changes in decomposition are intimately affected by the environment. "At a moderate temperature, a body is expected to start initial decay within a couple of days (5 p2)... while a cooler temperature generally slows down decomposition and a warmer one speeds it up." (Source: Majeres, J. 2003)
After temperature, chemical and bacterial factors of decomposition, insects are the next most important agents in the process. Assuming that the body is accessible to insects, they will increase the rate of decomposition dramatically. The most common inserts involved in the decomposition process include the fleshflies (Sarcophagidae) and blowflies (Calliphoridae). (Decomposition: Wikipedia)
The presence and life cycles of various insects, which is part of the field of forensic entomology, are used in forensic science to determine the time of death. This process is described as follows:
This method is based on the presence of various types of insects in the corpse. It is believed that when death occurs there is a universal death scent that attracts insects to the corpse. The first to arrive, within 10 minutes of death, are common green flies that feed on flesh and lay their eggs in the mouth, nose and ears. Twelve hours later these eggs hatch into maggots that feed on the dead tissues. (McLemore, J. 1993)
This process is known as PMI-postmortem interval where "an entomologist is able to identify the kind of insect and their stage of life to accurately predict how much time has gone by since insect activity began." (ibid)
The first insects that begin the decomposition process are usually the Diptera and "more specifically the Calliphoridae and Sarcophagidae." (ibid) The females of these flies deposits eggs or larvae in and around the natural orifices of the body, such as the eyes, ears, mouth, and nose and the eggs will also be deposited in any open wounds. (ibid) The insects hatch after about twelve hours and the small larvae begin to feed on the body tissues. (ibid)
After the maggots leave, some 24 to 36 hours after death, beetles arrive to eat the drying skin. Approximately 48 hours after death, other insects, such as spiders, mites and millipedes, arrive to feed on the insects on the corpse. Insects are collected from the remains and cultured to determine the species of insect and to assess their lifespans. The cycles of these insects are very precise and the time of death can be estimated with great accuracy. (McLemore, J. 1993)
There are many other ways that insects can help forensic science. They can be of assistance in determining whether the deceased died indoors or outdoors or during the night or day. Insects can also be used in toxilogical tests in order to determine the presence of drugs such as cocaine. (ibid)
Moisture and immersion in water also affects decomposition in radical ways. Many researchers feel that not enough research has been done on this aspect. This is the view of a study by MacDonell N. et al. entitled Aquatic Foresnics. The study states that findings from research conducted in 1983 point to the fact that "... one of the most important factors that will alter the normal course of insect succession in carrion is immersion fresh water. Many homicide victims are disposed of in bodies of water, which makes determining time of death extremely difficult. " (MacDonell. N. et al.)
The study stated that there has only been sufficient research on the effect of terrestrial insects on the body and not on the effect of the ecology of decomposition in fresh water. This points to the fact that there is a significant difference in the way that insects and fauna in water affect the decomposition process. As the study states, this is extremely important in terms of forensics and the decomposition process.
There are also other factors to be considered in the complex issue of water immersion. For example, if the body sinks and does not float, this will destroy all terrestrial insects. Water also serves to preserve the corpse as follows:
Bodies put in cold water or plastic bags sometimes experience adipocere. This is when the fat tissue just under the skin starts to saponify or turn into soap (5 p2). It takes a couple weeks to develop but will keep the body well preserved for months to years. The skin does not swell and turn green. Instead, it retains its natural color and the outermost layers of skin slip off. (Source: Majeres, J. 2003)
Although the process of decomposition begins at the time of death, the amount and the type of clothing worn by the deceased is another factor that affects decomposition and hence must be taken into account in forensic testing. Because heavier clothing helps retain body moisture it will have the effect of retarding decomposition. In lightly dressed bodies, the process of disarticulation is usually evident after a period of several months. (Rinehart, D.)
There is of course a great difference in the decomposition process with regard to buried and unburied bodies. Unburied bodies are exposed to many variables and factors that will generally accelerate the decomposing process. They usually show "... extreme decomposition due to the affects of temperature, climate, micro-organisms, insect and animal activity. (ibid)
General exposure to the climate and elements results in more extreme rates of decomposition. There are numerous factors which are forensically important in this regard. For example, the ground and leaf cover as well as seasonal changes all have an affect on the decomposition rate. There is also the factor of whether the body has been buried completely or only partially. These factors are also subject to the weather and the elements.
Partial or complete self-burial: disarticulated small bones and loosened teeth may 'sink' below the soil surface as it is worked by insects, rains and winds that can cause the mixing of earth, and decayed leaves which may cover bones (ibid) Other factors and characteristics of decomposition effect the eating and distribution of bodies and bones by carnivores which may make the forensic investigation extremely complex.
Another alternative to regular decomposition is mummification. This phenomenon occurs is hot, dry environments, which will preserve the corpse from decomposition for a long period of time.
Bacteria proliferation is limited due to dehydration of the body. It turns the skin dark, dry, and leathery. Mummification of the whole body occurs most times in the summer months and can take as little as a couple days to a week. Fingers and toes often mummify regardless of the temperature. Once a corpse is mummified, it is preserved for decades. (Majeres, J. 2003)
Chemistry. [Internet] Adipocere. Available at http://adipocere.homestead.com/chemistry.html [Accessed February 1, 2005.