Decomposition

The biological and chemical changes undergone by a body after death are known as decomposition. Decomposition is the continual process of gradual decay and disorganization of organic tissues and structures after death. Some tissues, such as bones, teeth, and hair, are more resistant to the action of microorganisms and other environmental factors and may last for centuries. Fossilized bones from animals and hominids, extinct millions of years ago, are studied today by paleontologists and anthropologists, thanks to such resilience.

Forensic medicine and forensic anthropology investigate the sequence and types of changes that affect decomposing bodies under different conditions and environments. A number of variables may affect both the rate and sequence of decomposition. Therefore, the estimation of time elapsed since death, known in forensics as the postmortem interval, takes into consideration the particular conditions associated with the decomposing body, such as temperature, level of humidity, and medium, such as exposure to preservatives, water, or soil.

For centuries, pigs were the animal model used to study both anatomy and the decomposition process due to their internal structural similarities to the human body. However, in 1980, the University of Tennessee at Knoxville began a research project on human decomposition with cadavers donated by the families of deceased persons or by the individuals who willed their bodies to science. In an area known as the Anthropological Research Facility, human bodies were laid to decompose in several different controlled conditions. These controlled experiments have significantly contributed to the better under-standing of human decomposition and to new levels of accuracy of forensic reconstruction techniques, such as the circumstances of death, time and cause of death , and determination of age, race, and gender. The data collected from several types of experiments and the measurements of each skeleton are recorded in a computer data bank named ForDisc (Forensic Discrimination).

A general description of postmortem changes due to decomposition basically includes two stages of autolysis, and four stages of putrefaction, besides some conservative phenomena such as saponification or adipocere , natural mummification, calcification, etc. However, these latter events only occur in specific conditions. Autolysis consists of the fast and intense spontaneous self-destruction of tissues by the body enzymes present in the cells, without any bacterial interference. Once cells stop receiving nutrients and oxygen via blood circulation, they start anaerobic (without oxygen) "breathing", breaking ATP (adenosine tri-phosphate) into ADP (adenosine di-phosphate) to obtain energy. Anaerobic respiration lasts for a few hours, until all ATP reserves are exhausted. The anaerobic respiration induces the accumulation of lactic acid in cell tissues that disrupts cell function. Enzymes then collapse the cell nucleus and cell breakdown (necrosis) occurs.

Tissues rich in blood vessels (more dependent on oxygen and energy) are the first ones to suffer autolysis, whereas those poorly irrigated or deprived from blood vessels, like the ocular corneas, are not immediately affected by decomposition. Putrefaction (or breakdown by microorganisms) follows autolysis. With the exception of fetuses and newly born babies, the main source of these microorganisms in corpses is the right part of the large intestines. Microorganisms then invade the abdominal cavity, the chest, head, and limbs. The first visible signs of such activity are the greenish abdominal stains, accompanied by the initial odors of rotting flesh. The stains gradually expand to other parts of the body (thorax, head, and limbs) and change from light to dark green, then beginning to blacken. In people who have drowned, the greenish coloration starts on the face, progresses toward the thoracic area, and then to other parts, due to the position that drowned bodies assume in water, which facilitates putrefaction of the upper respiratory pathways first. In newly born infants, putrefaction agents (bacteria, fungi, etc.) invade the body through all cavities, especially through the respiratory pathways. The greenish stains appear in newly born babies first on the face, neck, and chest due to bacterial activity in the upper and lower respiratory pathways, and because their intestines are sterile. This phase of decomposition is known as the chromatic period.

Bacterial action destroys the structure of cells and soft tissues, releasing in the process body fluids in internal cavities such as chest, abdomen, and oral tract. Anaerobic microorganisms produce methane, hydrogen sulphide, and other gases responsible for the increasing stench that surrounds rotting organic matter. As gases accumulate inside the body, it starts to swell, forcing more fluids from organs to internal cavities and blood to the periphery of the body. This phase of decomposition is called the gaseous period.

Subcutaneous (under the skin) blisters containing a mixture of plasma, hemoglobin , and gases appear and a marbled-like pattern spreads through the skin. The outer layers of the skin (epidermis) begin to detach from inner layers of the skin (dermis) as the gaseous period progresses. The subsequent phase involves the process of liquid putrefaction, in which the soft tissues are gradually dissolved. The body loses its shape as tissue mass decreases and the separation of skin layers is completed. During this liquefaction period, gases are released and a putrefied creamy substance covers the skeleton. The next phase is known as skeletonization, with the environmental elements (e.g., larvae, worms, and sometimes insects) separating the skeleton from ligaments, which causes the detachment of the skull , the mandible, and long bones, with bones eventually collapsing apart. Bones become increasingly fragile and lighter over the years, and acidic soils eventually dissolve them.

Adipocere (a waxy substance formed after death by fatty tissues) formation is not a universal phenomenon during decomposition. It is more common in remains of children, women, and overweight people, requiring both adipose (fatty) tissues and contact with humidity in the soil, or immersion in water, or the prevention of body water evaporation. Collective burial graves, were bodies are piled together, are also favorable to adipocere formation. Adipocere is very rare in remains of slim individuals because it results from the spontaneous chemical transformation of fatty tissues into a grayish-white waxy matter. Coroners have a special interest in adipocere because of its preservation properties of other tissues underneath. Adipocere-conserved body parts allow the performance of several forensic tests some months (and even years) after death. Examples are, the study of facial or neck lesions, toxicological tests, or the study of perforations caused by bullets.

Unborn fetuses that die between the sixth and the ninth months of pregnancy undergo a different process, known as maceration, due to prolonged exposure to the amniotic fluid. Fetal maceration external signs resemble in some ways those found in corpses immersed in water. However, the precise sequence of internal changes in fetal maceration is unique and offers three different well-defined phases or maceration degrees that allows the forensic determination of postmortem interval.

see also Adipocere; Autopsy; Bacterial biology; Body Farm; Crime scene reconstruction; Death, cause of; Drowning (signs of); Entomology; Exhumation; Immune system; Medical examiner; Mummies; Osteology and skeletal radiology; Toxicology.

Decomposition

Decomposition is the natural process by which large organic materials and molecules are broken down into simpler ones. The ultimate products of decomposition are simple molecules, such as carbon dioxide and water . Sometimes misunderstood as being undesirable, decomposition is actually an extremely vital ecological process. Living organisms are composed of cells and tissues, which are in turn made of complex organic molecules, including many that are large by molecular standards. Such large molecules are termed, macromolecules. Examples of macromolecules include cellulose , which comprises plant cell walls, triglyceride fats within animal cells, and proteins of plants, animals, fungi , protozoans, and bacteria . While alive, cells and whole organisms constantly maintain and add to the macromolecules necessary for life, in effect counteracting decomposition. Upon death, however, such maintenance and growth functions cease. Decomposition, then, begins the process of breaking cells down into their component molecules, and macromolecules into simpler organic and inorganic molecules. If decomposition did not occur, the world would be overcome with mountainous piles of dead biomass .

Decomposition is a process that recycles nutrients back to the soil from formerly living organisms. The process can involve soil organisms breaking-down large pieces of organic matter into smaller ones. Earthworms, insects , and snails are examples of animals involved in the initial stages of the decomposition process. Detritus is the term given to the disintegrated organic material produced by these animals. Earthworms are examples of detritivores, or organisms that consume detritus for energy . After larger particles are broken down, microorganisms further the decomposition process by secreting chemicals that digest organic material in detritus. The most prominent organisms that do this are bacteria and fungi. Bacteria and fungi that thrive in soil and feed upon dead organic matter are called saprophytes. Detritivores and saprophytes are essential in the recycling and disintegration processes of decomposition. The partially digested organic material left in soil, called humus , is then available for plants to use.

Humus is a soil component essential for plant growth. Found largely in topsoil, humus is created from dead living material in a process called humification. Humification of dead plant matter, for example, involves not only decomposition processes of detritivores, but also the physical action of weathering such as freezing, thawing, drying, and erosion . Humus is a major source of nutrients for plants. Essential minerals slowly leach from humus into the surrounding soil water, which are then absorbed by plant roots. Acting somewhat like a sponge, humus also helps retain soil moisture, while simultaneously keeping soil aerated by preventing compaction.

Humans can also make use of the natural process of decomposition. Composting is the gathering of waste organic material, most often plant material, into an aerated pile to facilitate partial decomposition into humus. The organic humus can then be used as a soil conditioner and fertilizer for gardens or on agricultural land. Normally, the process of decomposition can take a long time. However, in compost piles, the decomposition of organic matter is accelerated by turning to enhance oxygen availability, and by the build-up of heat and moisture. In compost piles, the action of saprophytes creates heat, which helps accelerate the entire process. The center of the compost pile is insulated from the exterior by the outer debris, and retains moisture well.

Terry Watkins

Decomposition

Decomposition is the natural process in which large organic (carbon-containing) materials and molecules are broken down into simpler ones. The process is driven by microorganisms. The ultimate products of decomposition are molecules such as carbon dioxide and water. Decomposition is an essential ecological process. Living organisms are composed of cells and tissues, which are in turn made of complex organic molecules, including many that are large by molecular standards. Such large molecules are termed macromolecules. Examples of macromolecules include cellulose, which comprises plant cell walls, triglyceride fats within animal cells, and proteins of plants, animals, fungi, protozoans, and bacteria. While alive, cells and whole organisms constantly maintain and add to the macromolecules necessary for life, in effect counteracting decomposition. Upon death, however, such maintenance and growth functions cease. Decomposition, then, begins the process of breaking cells down into their component molecules, and macromolecules into simpler organic and inorganic molecules. If decomposition did not occur, the world would be overcome with mountainous piles of dead biomass.

Decomposition is a process that recycles nutrients back to the soil from formerly living organisms. The process can involve soil organisms breaking-down large pieces of organic matter into smaller ones. Earthworms, insects, and snails are examples of animals involved in the initial stages of the decomposition process. Detritus is the term given to the disintegrated organic material produced by these animals. Earthworms are examples of detritivores, or organisms that consume detritus for energy. After larger particles are broken down, microorganisms further the decomposition process by secreting chemicals that digest organic material in detritus. The most prominent organisms that do this are bacteria and fungi. Bacteria and fungi that thrive in soil and feed upon dead organic matter are called saprophytes. Detritivores and saprophytes are essential in the recycling and disintegration processes of decomposition. The partially digested organic material left in soil, called humus, is then available for plants to use.

Humus is a soil component essential for plant growth. Found largely in topsoil, humus is created from dead living material in a process called humification. Humification of dead plant matter, for example, involves not only decomposition processes of detritivores, but also the physical action of weathering such as freezing, thawing, drying, and erosion. Humus is a major source of nutrients for plants. Essential minerals slowly leach from humus into the surrounding soil water, which are then absorbed by plant roots. Acting somewhat like a sponge, humus also helps retain soil moisture, while simultaneously keeping soil aerated by preventing compaction.

Humans can also make use of the natural process of decomposition. Composting is the gathering of waste

organic material, most often plant material, into an aerated pile to facilitate partial decomposition into humus. The organic humus can then be used as a soil conditioner and fertilizer for gardens or on agricultural land. Normally, the process of decomposition can take a long time. However, in compost piles, the decomposition of organic matter is accelerated by turning to enhance oxygen availability, and by the build-up of heat and moisture. In compost piles, the action of saprophytes creates heat, which helps accelerate the entire process. The center of the compost pile is insulated from the exterior by the outer debris, and retains moisture well.

Terry Watkins

Decomposition

Decomposition is the process by which dead organisms and their wastes are broken down into an organic form that is usable by other organisms. In ecological terms, the chemicals out of which living things are made were only borrowed from the earth, and when they die, they are returned by the process of decomposition. These chemicals are then recycled in order to be used by other living things.

Decomposition could be called rotting or decay, and it is carried out by a very important group of organisms called decomposers. Decomposers are bacteria and fungi as well as other small animals called detritivores. These decomposers break down waste and dead matter into smaller and smaller pieces until all the chemicals they contain are released into the air, water, and soil. Decomposers may be tiny in size but they are huge in numbers. In addition to bacteria and fungi, which are the most important decomposers, such larger animals as the slug, snail, earthworm, woodlouse, and centipede also play an important role in breaking down organic matter. A common example of a fungus and decomposer is a mushroom growing out of a dead tree trunk and feeding on the tree's decaying remains.

Decomposition is an essential stage in the cycling of nutrients through nature's food web (the connected network of producers, consumers, and decomposers). It is nature's way of recycling nutrients so they can be reused. Some of the major nutrients that are recycled include nitrogen, phosphorous, carbon, and oxygen. The decomposers that are a key link in nature's food web because they allow nutrients to be cycled through it continuously. If it were not for decomposers, the food web could not be self-sustaining and would break down because it would eventually have to obtain more nutrients from outside the ecosystem (an area in which living things interact with each other and the environment). For example, without the carbon dioxide that is released by decomposition, green plants would eventually die since they use it to make their food. Without green plants, there would be much less oxygen, since they give it off as part of the process of making their own food. No plants and no oxygen means that all animals would starve. Finally, without decomposition, the world would be a mineral-deficient land full of waste and corpses.

[See alsoBacteria; Fungi ]

Decomposition

The chemical and biochemical breakdown of a complex substance into its constituent compounds and elements, releasing energy, and often with the formation of new, simpler substances. Organic decomposition takes place mostly in or on the soil under aerobic conditions. Dead plant and animal materials are consumed by a myriad of organisms, from mice and moles, to worms and beetles, to fungi and bacteria. Enzymes produced by these organisms attack the decaying material, releasing water, carbon dioxide , nutrients, humus , and heat. New microbial cells are created in the process.

Decomposition is a major process in nutrient cycling, including the carbon and nitrogen cycles. The liberated carbon dioxide can be absorbed by photosynthetic organisms, including green plants, and made into new tissue in the photosynthesis process, or it can be used as a carbon source by autotrophic organisms.

Decomposition also acts on inorganic substances in a process called weathering . Minerals broken free from rocks by physical disintegration can chemically decompose by reacting with water and other chemicals to release elements, including potassium, calcium, magnesium, and iron. These and other elements can be taken up by plants and microorganisms , or they can remain in the soil system to react with other constituents, forming clays.