A skeleton in the bottom of a mock grave. The skeleton is partially jumbled up. There is a trowel and shovel at the edge of the grave.
A partially disarticulated skeleton (cast) excavated as part of forensic training.

What happens to human bodies after death?

Death, Decay and Decomposition

Before discussing the specific roles of forensic archaeologists and anthropologists in more detail, it is worth first considering what happens to a body after death.

After death, the human body undergoes a series of biological changes, collectively referred to as decomposition. These changes stem from two key factors:

  • the cessation of biological functions within the body

  • the spread and activity of bacteria after death.

As the soft tissues decay the skeleton is gradually exposed. The skeleton also undergoes changes following death, but can survive in the ground for centuries.

Four key stages of decomposition are presented below. Hypostasis, Algor Mortis and Rigor Mortis all occur as a result of normal biological functions stopping – particularly the cessation of blood flow and the cooling of the body. Putrefaction is the result of the spread of bacteria out of the gut and around the body. It causes swelling/bloating and is a key cause of the destruction of the soft tissue structures. The timelines for each phase below vary and should only be used as a very approximate indicator of the amount of time that has elapsed since death.

Phase 1: Hypostasis

This appears within an hour to several hours after death. The blood vessels collapse. Pooling of blood due to gravity can occur but will leave white gaps at pressure areas. Regurgitation of gastric contents can occur, as can the emission of semen.

Phase 2: Algor Mortis

This is the most useful indicator for estimating time of death in the first 24 hours. The body follows Newton’s Law of Cooling: The rate of cooling is proportional to the difference in temperature between the body surface and surrounding environment.

Phase 3: Rigor Mortis

For approximately the first 3 hours after death the body will be flaccid (soft) and warm. After about 3-8 hours is starts to stiffen, and from approximately 8-36 hours it will be stiff and cold. The body becomes stiff because of a range of chemical changes in the muscle fibres after death. After about 36 hours the chemical bonds resulting in the stiffness break down and the body will become soft again.

Phase 4: Putrefaction

This refers to the destruction of soft body tissues by bacterial action. It will usually occur 2-3 weeks after death.

  • 1st visible sign - discolouration of anterior abdominal wall skin

  • 2nd visible sign - superficial veins of skin visible; slippage of epidermis; putrid gas formation resulting in distended abdomen

  • 3rd visible sign - purge of putrid bloodstained fluid from body orifices.

Adipocere Formation and Mummification

These will only occur in certain environmental conditions.

Adipocere:

Sometimes referred to as ‘corpse wax’ or ‘grave-wax’. It is a waxy or soap-like substance and is only formed in moist conditions and in the presence of anaerobic bacteria, which decay (through hydrolysis) the fat to produce adipocere. It may occur in bodies deposited in waterlogged graves or by the side of a river. It is sometimes seen at 3-4 weeks after death, although 3 months is more typical.

Mummification:

Occurs when the body has been dried out. This may be the result of heat, but it can also be due to wind, or a draft in an attic. It results in the dehydration of the body and desiccation/brittleness of the skin. The internal organs can be either dried or putrefied depending on the conditions.

The Post Mortem Interval

The PMI is the amount of time that has elapsed since the person died. It’s very important for forensic investigators to establish because it will help narrow down the time-frame for a criminal investigation.

Archaeologists can help to establish the PMI because they can interpret factors relating to the depositional context of the body and its relationship with other features in the environment. For example, if the grave cuts through a sewerage pipe that the police know was dug in November 1983 and then a patio was built on top of the grave in April 1986, we know that the grave was dug sometime between November 1983 and April 1986. In this example, the sewerage pipe provides what is referred to as a terminus post quem (the earliest date that the body could have been deposited while the patio provides the terminus ante quem (the latest date that the body could have been buried). A famous example of a terminus ante quem is the eruption of Vesuvius in AD 79. Everything buried under the lava must have been present prior to the eruption.

Anthropologists can help to establish the PMI because they have expertise in understanding the rate at which a body will decompose within different environmental conditions. They will also understand the limitations of current techniques that attempt to estimate this within different environments.

Decomposition can be heavily influenced by an enormous number of variables referred to as taphonomic factors. These factors can speed up or slow down the decomposition process. For example, heat and insect activity will speed up the process, while cold temperatures or wrapping a body in plastic will slow it down. For buried human bodies, the acidity or alkalinity of the soil is also an important factor influencing bone preservation. Other factors such as whether the body was burned (cremated), or deposited in water will also have an impact. We will discuss these factors in a little more detail next week.

Individuals killed during periods of conflict are often buried in mass graves. The presence of multiple bodies within a single grave will also affect rates of decomposition. Bodies deposited at the same time within a mass grave will also decompose at different rates depending on their position within the grave and in relation to adjacent bodies. We will discuss the complexities of dealing with commingled deposits in Week 6.

Given all of these variables, it is therefore often very difficult to say with confidence how long the soft tissues will take to decompose after death. You can’t just look at a skeleton/decomposed body and provide a PMI.

When the soft tissues of the body are partially or fully decomposed, the person can no longer be recognised by family members. Identification of the dead person must then be carried out using scientific methods. These methods will be discussed in more detail in Week 3

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This article is from the free online course:

Forensic Archaeology and Anthropology

Durham University