Trace Evidence 2

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 • 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: 2.0-.05 mm • Silt: between 0.002 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 • 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.