Decomposition

Decomposition (or spoilage) refers to the reduction of the body of a formerly living organism into simpler forms of matter.

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Plant decomposition

See also: Compost and Anaerobic digestion

In most grassland ecosystems, fire is the primary mode of decomposition, making it crucial in nutrient cycling (DeBano et al. 1998). Also, fungi helps plants decompose.

Animal decomposition

  The body of a living organism begins to decompose (as part of a succession) shortly after death. Such decomposition can be simplified in two stages: In the first stage, it is limited to the production of vapors. In the second stage, liquid materials form and the flesh or plant matter begins to decompose. The science which studies such decomposition generally is called taphonomy.

Historically, the progression of decomposition of a living organism has been described as taking place in four stages: fresh (autolysis), bloat (putrefaction), decay (putrefaction and carnivores) and dry (diagenesis).

Process

Decomposition begins at the moment of death, caused by two factors: autolysis, the breaking down of tissues by the body's own internal chemicals and enzymes; and putrefaction, the breakdown of tissues by bacteria. These processes release gases that are the chief source of the characteristic odor of dead bodies. These gases swell the body.

Scavengers play an important role in decomposition. Insects and other animals are typically the next agent of decomposition, if the body is accessible to them. The most important insects that are typically involved in the process include the fleshflies (Sarcophagidae) and blowflies (Calliphoridae). The green-bottle fly seen in the summer is a blowfly. Larger scavengers, including coyotes, dogs, wolves, foxes, rats, and mice may eat a body if it is accessible to them. Some of these animals also remove and scatter bones.

Factors

The rate and manner of decomposition in an animal body is strongly affected by a number of factors. In roughly descending degrees of importance, they are:

• Temperature
• The availability of oxygen
• Prior embalming
• Cause of death
• Burial, and depth of burial
• Access by scavengers
• Trauma, including wounds and crushing blows
• Humidity, or wetness
• Rainfall
• Body size and weight
• Clothing
• The surface on which the body rests
• Foods/objects inside the specimens digestive tract (bacon compared to lettuce)

The speed at which decomposition occurs varies greatly. Factors such as temperature, humidity, and the season of death all determine how fast a fresh body will skeletonize or mummify. A basic guide for the effect of environment on decomposition is given as Casper's Law (or Ratio): when there is free access of air a body decomposes twice as fast than if immersed in water and eight times faster than if buried in earth.

The most important variable is a body's accessibility to insects, particularly flies. On the surface in tropical areas, invertebrates alone can easily reduce a fully fleshed corpse to clean bones in under two weeks. The skeleton itself is not permanent; acids in soils can reduce it to unrecognizable components. This is one reason given for the lack of human remains found in the wreckage of the Titanic, even in parts of the ship considered inaccessible to scavengers. Freshly skeletonized bone is often called "green" bone and has a characteristic greasy feel. Under certain conditions (normally cool, damp soil), bodies may undergo saponification and develop a waxy substance called adipocere, caused by the action of soil chemicals on the body's proteins and fats. The formation of adipocere slows decomposition by inhibiting the bacteria that cause putrefaction.

In extremely dry or cold conditions, the normal process of decomposition is halted — by either lack of moisture or temperature controls on bacterial and enzymatic action — causing the body to be preserved as a mummy. Frozen mummies commonly restart the decomposition process when thawed, whilst heat-desiccated mummies remain so unless exposed to moisture.

The bodies of newborns who never ingested food are an important exception to the normal process of decomposition. They lack the internal microbial flora that produce much of decomposition and quite commonly mummify if kept in even moderately dry conditions.

Embalming

Embalming is the practice of delaying decomposition of human and animal remains. Embalming slows decomposition somewhat, but does not forestall it indefinitely. Embalmers typically pay great attention to parts of the body seen by mourners, such as the face and hands. The chemicals used in embalming repel most insects, and slow down bacterial putrefaction by "fixing" cellular proteins, which means that they cannot act as a nutrient for bacteria, and killing the bacteria themselves.

In sufficiently dry environments, an embalmed body may end up mummified and it is not uncommon for bodies in dry vaults to remain preserved to a viewable extent after decades, such as the murdered civil rights activist Medgar Evers. Another case of this would be the body of Vladimir Lenin, who was kept submerged in a special tank of fluid for decades, almost perfectly preserved. Bodies submerged in peat bog may become naturally "embalmed", arresting decomposition and resulting in a preserved specimen known as a bog body. The body of Evita Peron was kept perfectly preserved for many years, and as far as is known, may still be so (her body is no longer on display as it once was).

The time for an embalmed body to be reduced to a skeleton varies greatly. Even when a body is decomposed, embalming treatment can still be achieved (the arterial system decays slower) but would not restore a natural appearance without extensive reconstruction and cosmetic work, and is largely used to control the foul odours due to decomposition.

Importance to forensics

Various sciences study the decomposition of bodies. These sciences fall under the general rubric of forensics, because the usual motive for study of the decomposition of human bodies is to determine the time and cause of death, for legal purposes:

• Forensic pathology studies the clues to the cause of death found in the corpse as a medical phenomenon
• Forensic entomology studies the insects and other vermin found in corpses; the sequence in which they appear, the kinds of insects, and where they are found in their life cycle are clues that can shed light on the time of death, the length of a corpse's exposure, and whether the corpse was moved.
• Forensic anthropology is the branch of physical anthropology that studies skeletons and human remains, usually to seek clues as to the identity, race, and sex of their former owner.

The Body Farm, at the University of Tennessee in Knoxville has a number of bodies laid out in various situations in a fenced-in plot near the medical center. Scientists at the University study how the human body decays in various circumstances to gain a better understanding into decomposition.

See also

• Cadaverine
• Putrescine
• Skeletonization (forensics)
• Staling