Human skeletal remains decay, a complex process influenced by many factors. This natural breakdown begins shortly after death, transforming organic components into simpler elements. While soft tissues decompose quickly, bones, being more durable, degrade more slowly but inevitably. The rate and extent of decay vary significantly, depending on the remains’ characteristics and the environment.
Initial Decomposition of Remains
Decomposition begins immediately after death with two internal processes: autolysis and putrefaction. Autolysis, or self-digestion, involves tissue breakdown by the body’s own enzymes, released from cells when circulation and oxygen cease. This process starts rapidly in metabolically active organs like the pancreas and stomach.
Following autolysis, putrefaction takes over, driven by bacteria and fungi, especially those from the gut and lungs, which proliferate throughout the body. This microbial action liquefies organs, muscles, and skin, producing gases that cause bloating. Insects, like blowflies, and larger scavengers also contribute, accelerating soft tissue removal. This active decay stage, where most soft tissues break down, results in significant mass loss and typically precedes skeletonization.
The Breakdown of Bone
Bones, though robust, are not immune to decay and undergo distinct decomposition processes. Bone has two main components: an organic matrix (primarily collagen) and an inorganic mineral phase (mainly hydroxyapatite). Both degrade through biological and chemical mechanisms.
Microbial activity, especially from bacteria, breaks down the organic collagen matrix within bone. These microorganisms create microscopic tunnels, known as bioerosion, within the bone structure as they consume organic material. Chemical processes concurrently affect the mineral component. Acids, generated by microbial activity or present in the environment, dissolve hydroxyapatite crystals. This dissolution weakens the bone’s structure, making it more susceptible to further degradation.
Environmental Factors Affecting Preservation
Skeletal decay rate and extent are heavily influenced by the environment. Temperature is a major factor; warmer climates accelerate decomposition due to increased microbial activity, while colder temperatures slow decay, sometimes leading to preservation through freezing or mummification.
Moisture levels also play a role; high humidity promotes microbial growth, while very dry conditions can lead to mummification, preserving tissues and bones. Soil pH is another variable, as acidic soils cause faster degradation of bone minerals. Oxygen availability is also important; anaerobic (low-oxygen) environments, such as waterlogged bogs or deep burials, inhibit microbial activity and promote remarkable preservation. Burial type, including depth and coffin presence, also affects preservation by influencing exposure to elements, insects, and microorganisms.
Long-Term Skeletal Changes
Over extended periods, beyond initial decay, skeletal remains undergo diagenesis. This refers to physical and chemical changes bones experience after burial, altering their original composition and structure. During diagenesis, chemical elements within the bone exchange with those in the surrounding soil, leading to mineral replacement. This process changes the bone’s internal structure and chemical makeup, even if its external shape remains intact.
An extreme form of long-term preservation is fossilization, where original bone material is gradually replaced by minerals from groundwater, effectively turning “bone to stone.” This process often involves bacteria precipitating minerals within the bone’s pores. While decay is an inevitable post-mortem process, specific environmental conditions and long-term diagenetic changes determine the ultimate state of preservation, ranging from complete disintegration to remarkable fossilization over millennia.