Trace Evidence 2
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Transcript Trace Evidence 2
Soil Science
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 worldwide
Largely the result of:
Weathering – decomposition or disintegration
Erosion – transport of material by wind/water
Parent material
Topography of an area
Length of time it takes for soil to form
Climate
Plants and animals
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
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
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
Use of a Munsell chart during a forensic geology investigation.