1. Soil Science
Trace Evidence 2

2. Soil and Forensics Used in much the same way as forensic geology
Soil represents a combination of geologic and biologic components
Classified much more scientifically than most think
Example: 70,000 different types are recognized

3. Soil and Forensics
May establish a relationship or link to the crime, the victim, or the suspect(s)
Physical properties—density, magnetism, particle size, mineralogy, petrology
Chemical properties—pH, trace elements

4. Soil and Forensics Types of earth materials are virtually unlimited
Wide distribution and can change over short distances
Statistical probability of a given sample having properties the same as another is very small
Evidence value of soil can be excellent

5. Soil Formation Factors
Defined as a combination of mineral and organic matter along with water and air that supports life
Covers most of the ground worldwide
Largely the result of:
Weathering – decomposition or disintegration
Erosion – transport of material by wind/water

6. Soil Formation Factors
Parent material
Topography of an area
Length of time it takes for soil to form
Climate
Plants and animals

7. Soil Components Parent material Humus Subsoil
The source of the weather material that produced the soil
Humus
Decayed plant/animal
Referred to as topsoil
Subsoil
Deeper soil layers
Minimal organic material

8. Soil Particle Sizes Soil can be classified by grain sizes
Gravel: >2.0 mm
Sand: mm
Silt: between and 0.05 mm
Clay: <.002 mm

9. Particle Size Classification
Accomplished by placing sample through a series of sieves
Percentages of each soil particle size are tallied and triangulated on a chart

11. Classification Almost always done by visual comparisons
Color and texture are the most important properties
Must be examined dry, wetness can change color
There are approx. 1,100 different soil colors
Requires use of microscopes
Dissecting microscopes are the most useful

12. Color Classification
Reds/yellows are created by iron content in the soil
Dark brown/black are created by high amounts of organic material
Usually based on the Munsell color chart
The basis for most computer graphics models

13. Color Classification RGB Values
Based on amounts of Red, Green and Blue hues
Require specific computerized devices for accurate measurements
“eyeball” measurements can also be made since human eye is very sensitive to color
Usually expressed in 3 values from 0-255

14. Color Classification
An RGB color wheel. For example, Pure White would be indicated as R=255, G=255, B=255. Pure black would be R=0, G=0, B=0. The color in the box below could be reproduced on a computer with R=73, G=0, B=238

15. Munsell Color Chart Hue Value Chroma Based on five main values
Red, Yellow, Green, Blue, Purple
Value
A factor of lightness
“10” = White, “0” = Black
Chroma
“Purity” of color

16. Munsell Color Chart

17. Color Classification
Use of a Munsell chart during a forensic geology investigation.