Soil
Definition
Weathered surface layer of earth made of mineral particles, organic matter (humus), water, air and living micro-organisms. The forensic interest is in the mineral and organic fractions plus any anthropogenic inclusions (paint flakes, glass shards, fibres).
- Composition
- Minerals, organic matter, water, air, microbes
- Location
- Weathered surface layer of earth
- Forensic interest
- Mineral/organic fraction plus anthropogenic inclusions
- Example inclusions
- Paint flakes, glass shards, fibres
Common questions
Why do anthropogenic inclusions matter as much as the natural soil fraction in forensic work?+
Man-made inclusions such as paint chips, glass fragments, or fibres can be highly specific to a particular location or event, sometimes providing stronger individualising evidence than the natural mineral composition, which tends to be shared over a wider area.
Can soil evidence identify an exact location, or only a general type of area?+
It depends on how distinctive the sample is. Soil comparison is generally an exclusionary or associative tool, showing consistency or inconsistency between a questioned and a known sample, rather than pinpointing an exact GPS location on its own; specificity improves when the sample includes unusual mineral or anthropogenic components.
How quickly can surface soil composition change at a given site?+
The mineral fraction is relatively stable over time, but the organic and microbial components can shift seasonally and with disturbance, which is why comparison samples are ideally collected close in time to the questioned sample and from a matched depth.
Related terms
- Density-Gradient Column
- Glass column filled with stepwise layers of liquids of decreasing density (commonly bromoform 2.89 g/cm3 and bromobenzene 1.50 g/cm3 mixed in known...
- Loss on Ignition (LOI)
- Weight loss after heating dried soil to 550 degrees Celsius. Approximates the organic matter content. A simple, cheap, high-yield discriminator in field...
- Munsell Soil Colour
- Standardised colour notation written as hue, value and chroma (e.g. 10YR 4/3 dark brown). Read by holding a moist soil sample against...
- Regur (Black Cotton Soil)
- Indian Vertisol formed on Deccan basalt. High in smectite (montmorillonite) clay, deep black colour, swells and shrinks dramatically with moisture. Major signature...
- USDA Texture Triangle
- Ternary diagram that classifies soils by relative proportion of sand (2.0 to 0.05 mm), silt (0.05 to 0.002 mm) and clay (less...
- XRD
- X-ray diffraction. Identifies crystalline mineral phases (quartz, feldspar, kaolinite, montmorillonite, calcite) by their characteristic d-spacings via Bragg's law. The mineral assemblage is...
- XRF and ICP-MS
- Elemental techniques for the trace-metal fingerprint (Fe, Ti, Mn, Cr, Ni, V, rare earths). XRF (often EDXRF) is non-destructive; ICP-MS is destructive...