1. Using Soil to Solve Crimes

2. Definition of soil for forensics:
Any disintegrated surface material, both natural and artificial, that lies on or near the earth’s surface
Physical trace evidence
Includes naturally occurring rocks, minerals, vegetation, and animal matter; as well as glass, paint chips, asphalt, brick fragments, cinders

3. Usefulness of soil evidence:
Prevalent at crime scenes
Unique to a particular location
High transferability between the scene and the criminal
Can link a suspect or object to the scene

4. Collection methods:
Collect samples at various intervals within a 100-yard radius of the crime scene
Collect samples at all possible alibi locations the suspect gives
Collect only the surface layer in most cases
Because there is variation of soil even at a particular location, it is important to collect standard/reference samples at various intervals.
Need a representative sample of the soil.

5. Preservation methods:
Soil collected at a site:
Packaged in individual containers
Soil collected from an object:
Individually wrapped in paper
Clumps of soil must remain intact
Individual containers such as a plastic vial
Vials need to be marked with the location where the sample was made
Soil should remain intact on object
Paper bags may be used for objects – collects any soil that may accidentally fall off in transport
Clumps of soil in the case of a car shows order in which the soil adhered to the car (layering effect)

6. Analysis methods: Comparison of suspect/ object to the crime scene
Need 1-2 tablespoons of sample
Sample must be dry
Samples must be dried under identical laboratory conditions

7. Analysis methods: Geological maps
Using the characteristics of the sample and with knowledge of local geography geologists can direct police to the general vicinity where the soil originates

8. Analysis methods: Visual comparison of color & texture
Munsell soil color chart books
Nearly 1100 distinguishable soil colors
The percentage of sand, silt, and clay will determine the soil texture. Can give students samples of clay, sand, and silt to feel the difference in texture.

9. Analysis methods: Microscopic examination
Low power: Animal & plant material, artificial debris
High power: Minerals and rocks
Can provide the most varied and significant points of comparison between soil samples
Minerals: naturally occurring crystals: physical properties (color, geometric shape, density, and refractive index) most useful for identification
2200 minerals known to exist

10. Analysis methods: Density-gradient tube Glass tube
Filled with 6-10 layers of liquids with different densities
Soil particles sink to portion of tube with similar density
Ask students what a gradient is
Useful in combination with other tests since many soils collected from different locations yield similar density distribution patterns