What Is Soil?
• Mixture of organic and inorganic material• May range from 100% inorganic (sand) to
nearly 100% organic (peat)• Inorganic part is minerals• Organic part is decayed plant and animal
material and is sometimes called humus
Forensic Significance of Soil• Soil is class evidence - cannot be
individualized to a particular location–There is no classification system for
soils–Soils can be easily transported–Soils within a few meters horizontally
or vertically differ
Forensic Geology In Intelligence Work
Remember the outcrop you saw behind Osama bin Laden on TV after September 11. What was the location?
A geologist who has done field work in the area would be able to locate that outcrop, and that actually happened: Geologist John Shroder was able to identify the region where bin Laden had been sighted in Afghanistan in 2001 (see Geotimes, February 2002).
Properties of SoilProperties of Soil• Soil includes the disintegrated surfaces material
that is found on or near the Earth's surface.• Soil can include:
• RocksRocks• MineralsMinerals• VegetationVegetation• Animal matterAnimal matter• GlassGlass• Paint chipsPaint chips• AsphaltAsphalt• BrickBrick
Physical Properties of Soil
– Soil Texture, Structure, Compaction• is the percent of sand, silt and clay in a soil. – sand is the coarsest (0.06 - 2 mm) – silt is intermediate (0.002 - 0.06 mm) – clay is the finest (<0.002 mm)
Soil Texture
• The texture of a soil is determined by the percentages of particles like sand, silt, & clay that it contains.
How is Soil Analyzed?How is Soil Analyzed?
• Color comparisons of dry samples under identical conditions – You want dry soil because wet soil is darker.
• Microscopic examination for debris.
• Geologically for rocks and minerals.
• Density-Gradient Tube Technique