trace evidence 2
Post on 09-Feb-2016
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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
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
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
Defined as a combination of mineral and organic matter along with water and air that supports life
Covers most of the ground worldwideLargely the result of:
Weathering – decomposition or disintegration
Erosion – transport of material by wind/water
Parent materialTopography of an areaLength of time it takes for soil to
formClimatePlants and animals
Parent material The source of the weather material
that produced the soilHumus
Decayed plant/animal Referred to as topsoil
Subsoil Deeper soil layers Minimal organic material
Soil can be classified by grain sizesGravel: >2.0 mmSand: 2.0-.05 mmSilt: between 0.002 and 0.05 mm Clay: <.002 mm
Accomplished by placing sample through a series of sieves
Percentages of each soil particle size are tallied and triangulated on a chart
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
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
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
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
Hue Based on five main values Red, Yellow, Green, Blue, Purple
Value A factor of lightness “10” = White, “0” = Black
Chroma “Purity” of color
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