Soil Science Trace Evidence 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

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

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

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

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

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

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

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

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

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

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

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

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

Munsell Color Chart

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