Nobody knows what happens after you die, but one thing is certain: the natural process of human decomposition — the postmortem decay of tissue and muscle.
Despite the process of decomposition beginning immediately upon death, some western cultures delay its progression through embalming. Embalming is a custom, used mainly in the US and Canada, that temporarily preserves a deceased body so it will be intact for viewing at wakes and funerals. The way in which the corpse is embalmed greatly affects the duration of its preservation. There is no public health benefit to embalming and it is practiced purely for cosmetic purposes; however, in some places, it is prohibited to embalm a person who died from a serious contagious disease.
The rate of decomposition is largely dependent on the cause of death, the weight of the deceased and other environmental factors. For example, bodies decay at a faster rate if they are exposed to the elements or wildlife, if they are in warm environments, or if they are under water. This is why forensic scientists created body farms warning: article contains image of human decomposition to study human decomposition rates under various conditions.
The two most recently placed bodies are spread-eagled near the centre of the small enclosure with much of their loose, grey-blue mottled skin still intact, their ribcages and pelvic bones visible between slowly putrefying flesh. A few metres away lies another, fully skeletonised, with its black, hardened skin clinging to the bones, as if it were wearing a shiny latex suit and skullcap.
Further still, beyond other skeletal remains scattered by vultures, lies a third body within a wood and wire cage. It is nearing the end of the death cycle, partly mummified. Several large, brown mushrooms grow from where an abdomen once was. For most of us the sight of a rotting corpse is at best unsettling and at worst repulsive and frightening, the stuff of nightmares. Within it, a nine-acre plot of densely wooded land has been sealed off from the wider area and further subdivided, by foot-high green wire fences topped with barbed wire.
In late , SHSU researchers Sibyl Bucheli and Aaron Lynne and their colleagues placed two fresh cadavers here, and left them to decay under natural conditions. Once self-digestion is under way and bacteria have started to escape from the gastrointestinal tract, putrefaction begins. This is molecular death — the breakdown of soft tissues even further, into gases, liquids and salts. It is already under way at the earlier stages of decomposition but really gets going when anaerobic bacteria get in on the act.
Every dead body is likely to have its own unique microbial signature Credit: Science Photo Library. Putrefaction is associated with a marked shift from aerobic bacterial species, which require oxygen to grow, to anaerobic ones, which do not. This causes further discolouration of the body. As damaged blood cells continue to leak from disintegrating vessels, anaerobic bacteria convert haemoglobin molecules, which once carried oxygen around the body, into sulfhaemoglobin.
The presence of this molecule in settled blood gives skin the marbled, greenish-black appearance characteristic of a body undergoing active decomposition. As the gas pressure continues to build up inside the body, it causes blisters to appear all over the skin surface.
Eventually, the gases and liquefied tissues purge from the body, usually leaking from the anus and other orifices and frequently also leaking from ripped skin in other parts of the body.
Sometimes, the pressure is so great that the abdomen bursts open. Bloating is often used as a marker for the transition between early and later stages of decomposition, and another recent study shows that this transition is characterised by a distinct shift in the composition of cadaveric bacteria.
Bucheli and Lynne took samples of bacteria from various parts of the bodies at the beginning and the end of the bloat stage.
They then extracted bacterial DNA from the samples and sequenced it. Flies lay eggs on a cadaver in the hours after death, either in orifices or open wounds Credit: Science Photo Library. As an entomologist, Bucheli is mainly interested in the insects that colonise cadavers. When a decomposing body starts to purge, it becomes fully exposed to its surroundings. Two species closely linked with decomposition are blowflies and flesh flies and their larvae. Cadavers give off a foul, sickly-sweet odour, made up of a complex cocktail of volatile compounds which changes as decomposition progresses.
Blowflies detect the smell using specialised receptors on their antennae, then land on the cadaver and lay their eggs in orifices and open wounds. Each fly deposits around eggs that hatch within 24 hours, giving rise to small first-stage maggots. These feed on the rotting flesh and then moult into larger maggots, which feed for several hours before moulting again.
After feeding some more, these yet larger, and now fattened, maggots wriggle away from the body. Wriggling maggots generate an enormous amount of heat within the body Credit: Science Photo Library. Under the right conditions, an actively decaying body will have large numbers of stage-three maggots feeding on it. Like penguins huddling in the South Pole, individual maggots within the mass are constantly on the move.
But whereas penguins huddle to keep warm, maggots in the mass move around to stay cool. Vultures and other scavengers, as well as other large meat-eating animals, may also descend upon the body. In the absence of scavengers, though, the maggots are responsible for removal of the soft tissues. Third-stage maggots will move away from a cadaver in large numbers, often following the same route.
Their activity is so rigorous that their migration paths may be seen after decomposition is finished, as deep furrows in the soil emanating from the cadaver. Every species that visits a cadaver has a unique repertoire of gut microbes, and different types of soil are likely to harbour distinct bacterial communities — the composition of which is probably determined by factors such as temperature, moisture, and the soil type and texture.
Although an exposed human body in optimum conditions can be reduced to bone in 10 days, a body that is buried 1. However, the larvae of some blowflies and flesh flies, can easily locate and burrow down to bodies buried at 0. Adult coffin flies can burrow 0. If insects are excluded and the body decays slowly, other chemical reactions take place. Grave wax adipocere accumulates on the surface of a buried body if fatty deposits are permitted to break down slowly. Bacteria can never be excluded because they are present in the intestine before death.
However, the environment can be made unsuitable for bacterial activity by rapid drying of a body mummification or the introduction of bactericides embalming. Similarly, freezing of bodies cryonics will prevent decay. The time taken for a body to decompose depends on climatic conditions, like temperature and moisture, as well as the accessibility to insects.
In summer, a human body in an exposed location can be reduced to bones alone in just nine days. The Australian Museum respects and acknowledges the Gadigal people as the First Peoples and Traditional Custodians of the land and waterways on which the Museum stands. Image credit: gadigal yilimung shield made by Uncle Charles Chicka Madden.
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What is grave wax? Decomposition - Cheating the decomposers Insects Bacteria Time is variable. Defining death There are three main ways that death can be defined: legally, culturally or clinically. Find out more. Stages of decomposition Initial decay Putrefaction Butyric fermentation.
Body cells no longer receive supplies of blood and oxygen. Blood drains from capillaries in the upper surfaces and collects in the blood vessels in the lower surfaces.
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