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 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

http://upload.wikimedia.org/wikipedia/commons/d/d5/Munsell-system.svg

Use of a Munsell chart during a forensic geology investigation.