Decomposition is the natural breakdown of organic matter following death, returning complex biological structures to simpler elements. The timeline for this transformation is highly variable and dependent on surrounding conditions. Decomposition is driven by two simultaneous biological actions: autolysis and putrefaction. Autolysis is the internal self-digestion where the body’s own enzymes, released from ruptured cells, begin to break down tissues. Putrefaction is the decomposition of tissues resulting from the metabolic activity of bacteria and other microorganisms, primarily those originating in the gut.
The Initial Stages and Timeline
The initial post-mortem period, known as the fresh stage, begins immediately after death with a series of physical changes. The first is Algor Mortis, the cooling of the body to match the ambient environmental temperature, which helps estimate the time since death.
Livor Mortis, or lividity, begins as blood settles due to gravity once circulation stops. This pooling causes a purplish-red discoloration in the lowest parts of the body, starting within two to four hours and becoming fixed after eight to twelve hours.
The third major change is Rigor Mortis, the stiffening of muscles caused by the depletion of ATP, the energy molecule necessary for muscle relaxation. Rigor Mortis usually begins within two hours, is fully established by eight to twelve hours, and typically passes completely by 36 hours post-mortem. This initial phase, lasting between 24 and 72 hours, ends when microbial activity begins, marking the transition to decay.
Stages of Decay and Associated Timeframes
The first major physical transformation driven by microbial action is the Bloat stage, which generally begins two to six days after death in a temperate environment. During this phase, anaerobic bacteria ferment carbohydrates and proteins, producing large volumes of gases like hydrogen sulfide and methane. The buildup of these gases causes the body to swell significantly, leading to a distended appearance.
The internal gas pressure can cause fluids to leak and the skin to become discolored, often a greenish hue. This stage produces the strong odor characteristic of decomposition, attracting blowflies to lay eggs. The resulting fly larvae, or maggots, dramatically accelerate the breakdown of soft tissue.
Following the rupture of bloated tissues and the release of gases, the body enters the Active Decay stage, typically starting between five and eleven days post-mortem. This phase is marked by the most rapid loss of tissue mass as organs, muscles, and skin begin to liquefy. The massive feeding activity of insect larvae, combined with bacterial action, results in the body losing its structural integrity.
The Active Decay phase transitions into Advanced Decay, which can begin around 10 to 25 days after death. By this point, most soft tissues have been consumed or broken down, and the rate of decay slows considerably. The body collapses as internal fluids drain, leaving behind a reduced mass of dried tissue, skin, hair, and bone.
Environmental Factors That Accelerate or Slow Decomposition
The timelines for decay are generalizations based on a body exposed on the surface in a moderate climate. The single most influential factor affecting the rate of decomposition is temperature. Warm temperatures significantly accelerate the metabolic rates of enzymes and microorganisms, speeding up the entire process. Conversely, cold temperatures slow or virtually halt decay, a principle utilized in refrigeration.
Moisture and humidity are also important, as microbial activity requires water. A body in a hot, humid environment decomposes much faster than one in a hot, arid environment, where lack of moisture can lead to mummification. However, saturated conditions, such as a deep peat bog, can also slow decomposition due to lack of oxygen, sometimes preserving soft tissue.
The environment of deposition determines which external agents contribute to decay. A body submerged in water generally decomposes slower than one exposed to air; one week in air is roughly equivalent to two weeks in water. Burial also dramatically slows the process by providing protection from insects and maintaining cooler, stable temperatures. Deep burial in dense, cool soil excludes oxygen and insects, extending the decomposition timeline significantly.
Skeletonization and Final Disposition
Skeletonization is the final stage of the decomposition timeline, marking the point at which all soft tissues have been removed, leaving only the skeletal structure. The onset of this stage is highly variable, potentially occurring within weeks in hot, insect-rich tropical environments, but often taking months or several years in temperate or protected settings.
Once skeletonized, the fate of the bones depends entirely on the surrounding soil and environment. The long-term breakdown of the skeletal material is known as diagenesis. This involves the decay of the organic component (collagen) and the dissolution of the inorganic mineral structure. This process is extremely slow, taking decades to centuries for bones to fully disintegrate in fertile, acidic soil. In neutral-pH soil, dry sand, or highly anoxic environments, bones can persist for hundreds of years, sometimes leading to fossilization.