Trace Evidence 2

download report

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.