The term (Taphonomy) was first introduced by the Russian geologist Efremov it referred to the (Transition of animal or plant remains from the biosphere into the lithosphere ) the word is derived from the Greek word meaning taphos (burial) and nomos (law).This term has been variously applied to a wide range of studies in palaeontology, paleoanthropology, paleoecology and archaeology. Taphonomic phenomena are grouped into two phases, Bipstratinomy is the events that occur between the death of the organism and the burial, and Diagenesis is the event that occurs after the burial since Efremov's definition of taphonomy has expanded to include the fossilization of organic and inorganic material through both cultural and environmental influences [1]. Given the increased number of factors influencing both quantitatively and qualitatively the dynamics of the cadaveric chemical decomposition, there is a need for extensive studies regarding these processes studies which need to consider as many variables. However, human taphonomy studies require particular condition, especially arranged facilities, which can reproduce as precisely as possible different conditions in which the decomposition of human bodies may take place [2]. Figure 1 explained taphonomy is the study of the transition of organic remains and traces from the biosphere to the lithosphere.

Figure 1: Represent Illustrates Alternative Pathways in this Transition.

Taphonomy  can  be  divided into different  stages  in  the  progression  of  remains  from biosphere to lithosphere (Figure 2).  A common three-part categorization is: 1- necrology-early post-mortem processes such as scavenging and decomposition, 2-biostratinomy-transport and burial and 3- diagenesis-changes that usually occur after burial, such as mineralization [3].

Figure 2: Three-Part Categorization Stages in the Progression of Remains from Biosphere to Lithosphere.

Major stages ( top to bottom) that organic remains pass through (left) before becoming part of the fossil record, sub-disciplines of the field of Taphonomy (right), with the estimated relative importance of biological (green) versus geological (tan) for each stage (centre). During life, an organism has control over its body, but after death, other biological processes take over to break down tissues and recycle nutrients. Geological processes usually become more important over time as biological processes taper off. Solid lines indicate the main focus in the sequence of stages of the three sub-disciplines of taphonomy, and dashed lines show variability when different taphonomic processes can affect organic remains. Ultimately the survival of buried fossils (mineralized or not) in the geological record is subject to tectonic controls on the fate of depositional basins.

The human body is a complex of organic (proteins, lipids, carbohydrates), which undergo chemical decomposition processes soon after death. The compounds released during decomposition characterize the development of different stages of this process, eg: biogenic amines resulting from the decomposition of the proteins will confer the particular smell of the cadaver, gases resulting from carbohydrate fermentation will give the bloating aspect of the cadaver [4].

The postmortem decomposition evolves in two main phases: the first one is autolysis which consists of the enzymatic self–digesting of the cells and paves the way for the second phase i.e putrefaction. Table 1 represent decomposition stages and the physical appearance of remains at each staget,the trigger for these processes is cell anoxia-cessation of oxygen delivery to the cells which intervenes between the cell membranes and junction destroying them, the enzymes and the entire content of the cells being released. Lack of oxygen also creates optimal conditions for the development of anaerobic bacteria in the gastrointestinal and respiratory tracts, such as Bacteroides and Clostridium [5,6].

Living organisms are complex heterogeneous structures, the parts of which differ in size, shape and composition. Because of these differences, the different components of an organism do not behave similarly during predation and after death and because organisms are different, these behaviours also differ when different species are taken into account. Thus, organisms become preserved, fossilized or destroyed. Probably no fossil biota is preserved bias-free, even those where skins, soft tissues or colours are still visible [7,8].

Table 1: Decomposition Stages and the Physical Appearance of Remains at Each Stage [9].

The decomposition process follows the same stage in every corpse, but the particularities of the body and the adjacent environment make it happen at different moments time table 2 represents the relationship between the body and environment [10].

Table 2: Factors Affecting the Rate of Cadaveric Chemical Decomposition [11].

Particularities of the body comprise; clothing, age, body mass, body dimension , gastric content, hydration state and nutritional state before death , as well as cause of death [12,13]. Regarding the latter , the sepsis which maintains the body temperature at high levels ,asphyxia when the blood remains in a liquid phase favoring the spread of bacteria or congestive heart failure which confers a high level of internal hydration by edema , hasten the process of putrefaction [14,15]. Characteristics of the environment in which the body stays and which are relevant for the development of the chemical decomposition are: temperature, humidity, pH and composition of the soil in case of buried corpses. Decomposition in corpses sitting outdoor is significantly influenced by the activity of insects, rodent, carnivores and the stream of air as well as the rainfall [16].

Humidity in the environment and inside the body (antemortem hydration, congestive heart failure) hastens the putrefaction process, decomposition is also speeded up by obesity and warm clothes. On the contrary,this process is delayed by tight clothes and placing the corpse on metallic surface [17]. Temperature and humidity also influence the profile of the volatile compounds released during the putrefaction process in two ways :first by the direct effect they have on the breakdown of protein and carbohydrates and second by influencing the type of microorganism in soil and insects which colonize the body [18].

The profile of the volatile compounds generated during the chemical decomposition is also influenced by different species of bacteria , such as C.aminovalericum which produces acetone, ethanol and 1-butanol and C.cadaveris which produces in addition isobutanol, n-butanol, isoamyl alcohol and n-amyl alcohol .The presence of larvaeemerged after scavenger insects oviposition contributes in addition to the destruction of the tissues ,low temperature will gather less insects which will destroy less cadaveric material , leaving more tissue for chemical conversion by bacterial activity , leading further on to successive leakage of the fatty volatile acids in the soil [2,4].The fact that human postmortem decomposition is a process and not a solitary event is proved by the release of several volatile compounds in certain PMI or by the presence of multiple stages of decomposition on the same corpse at the same time [13].

Putrefaction, both transformative and destructive process implies progressive disintegration of the organic compounds from the tissue to form gases, liquids and salts. Unlike autolysis putrefaction is noticeable on the external examination of the body since its beginning by different aspects such as color changes and peculiar odors and bloating of the body ,the ground for these changes being prepared both by autolysis and by different microorganism ;bacteria , fungi and protozoa. The release of different volatile compounds during putrefaction determines specific odors ammonia has pungent smell, hydrogen sulfied smells like rotten eggs, sulfur dioxide has an irritating and pungent odor, indole and skatole-facal and nauseating odor, cadaverine-putrid and decaying flesh odor, putrescine-putrid and nauseating odor [2].

During the chemical process of postmortem decomposition a number of gases will evolve (CO2CH4, NH3H2S,SO2 and H2), resulting in the distention of the tissues, further on the pressure inside the body will increase and the purging fluid will be expelled ,first through oral and nasal cavities and then through every opening of the body  [7].

The distension of the body in this stage may determine ruptures of the skin , and together with the destructions resulting from larval activity the tissues will be receiving new oxygen from the environment and the activity of the aerobic microorganism will be resumed ,withal , the gases evolving inside the abdominal cavity will elevate the diaphragm ,increasing pressure inside the thoracic cavity and as a consequence the air will mix the putrefaction fluid with the expulsion of reddish foam from nose and mouth[19].

Forensic taphonomy requires interdisciplinary input from biology, archeologys, anthropologist, entomologist, botanists and geologist among others. There are five main stages of taphonomy a-disarticulation b-dispersal c-accumulation d-fossilization e-mechanical alteration, changes during the first stage of cadavers chemical decomposition cannot be seen with the naked eye but the microscope examination reveals the gradual fainting of the cells and tissues structure,corpses spread out particular odors since the very first minutes after death [20].

These initial odor cannot be perceived by human senses, but the flies have the capacity to sense them due to their antennas with special functions, thus,in the early stage of decomposition flies will populate the corpse and lay eggs especially around the orifices [21]. The first sign of putrefaction at gross examination is the greenish coloration of the skin in the right iliac fossa ,the specific location is due to the close contact between the caecum and the skin at this level ,while the peculiar color is given by sulfhemoglobin ,arisen from the hemolysed hemoglobin coupled with the hydrogen sulfied generated by bacteria from the intestines ,combining the enzymatic action during the breakdown of erythrocytes with the bacterial action producing hydrogen sulfied , a dark color residue will form which will be deposed on blood vessel walls and subsequently in the tissues giving the mottled aspect of the skin [19].

Cadaveric decomposition ends with skeletonizing , a phase which sometime needs days or months and sometimes years to be reached while the complete disappearance of corpse may need hundreds of years(14).The metabolism of the aerobic bacteria which are normally present inside digestive tract and respiratory system exhausts the minimum oxygen remaining in the body following cessation of the cardiac activity (20),and the ground will become propitious for anaerobic organism such as Bacteroides , Clostridia , Streptococci species which will enable the conversion of proteins ,carbohydrates and lipids to different organic acids and gases [22,23].

Studies into human decomposition helps answer four questions :who is the victim , how did the victim die , where and when did the victim die ?in addition to being extremely useful for “Time Since Death” determinations, the identification of decompostional products may also be relevant to victim identification. Buried bodies normally decompose slower than bodies on the surface due to a-less exposure to scavengers and insects b-temperature fluctuates less the deeper the body is in grave c- less exposure to weather d- compaction of soil e- difference in PH due to decaying matter f- moisture level.

The estimation of postmortem interval and the reconstruction of the death event heavily rely on the knowledge of early and late postmortem changes, the chemical processes occurring during the human cadaver decomposition generate numerous chemical compounds, and the type and rate of their occurrence depending on several factors, either concerning the cadaver characteristics or the characteristics of the environment the cadaver stays.

Identification and analysis of the chemical compound that emerged after human decomposition (gases, liquid, and salts) give valuable information to forensic pathologists for estimating the postmortem interval (PMI) given the increased number of factors influencing both quantitatively and qualitatively the dynamic of the cadaveric chemical decomposition, there is a need for extensive studies regarding these processes. However, human taphonomy studies require particular conditions, in specially arranged facilities, which can reproduce as precisely as possible different conditions in which the decomposition of human bodies may take place.

In summer, a human body in an exposed location can be reduced to bones alone in just nine days. Current techniques to determine the post-mortem interval using decompositional products (volatile fatty acids) can range from ± 2 days for soft tissue decay and ± weeks using inorganics for skeletonized material, up to approximately 5 years. Currently, studies looking at specific organ biomarkers, which it hopes will narrow the estimated range down to less than 12 hours for the first several weeks of decomposition. Novel fingerprint and DNA recovery techniques will aid in both victim and perpetrator identification all of which are made possible by an intimate knowledge of the decomposition process.  

Recommendation

The understanding of chemical postmortem changes is a crucial step in the estimation of the PMI, still establishing the PMI is less accurate as decomposition progresses, thus being necessary to corroborate as many parameters as possible .The time taken for a body to decompose depends on climatic condition, like temperature and moisture, as well as the accessibility to insects.

Declarations

I certify that the information given is true and complete to the best of my knowledge. I understand that if I have deliberately given any false information or have withheld any information regarding any situation, I am liable for prosecution for fraud and/or perjury.

Ethics approval and consent to participate

This study was approved form scientific and ethical council in the Iraqi medical legal directorate (MLD) / Ministry of Health (MOH). This research was conducted based on Article 2 of the Iraqi Forensic Medicine Law of 2013.

Consent for publication

This review article was dependent on up to date systematic review articles in Forensic Human Taphonomy and article was consent for publication conducted based on Article 2 of the Iraqi Forensic Medicine Law of 2013.

Availability of data and material

This depend on up to date data publication from International Commission on Missing Person ICMP and CAMBRIDGE University Press with many of global studies.

Competing interests

The author declare that they have no conflict of interest.

Funding

The author did not receive support from any organization for the submitted work. No funding was received to assist with the preparation of this manuscript. No funding was received for conducting this study.

Authors' contributions

The author confirms sole responsibility for the following: study conception and design, data collection, analysis and interpretation of results, and manuscript preparation.

Acknowledgements

The author wishes to thank Dr. Shakir Mahmood Muhammed Editor - in - Chief / Iraqi New Medical Journal for their reviewer of this article.

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