Soil Evidence

Cases involving Soil Evidence

Forensic Geology• Rocks, minerals, soils and related materials

have evidential value.  The value lies in the almost unlimited number of kinds of materials and the large number of measurements and observations that we can make on these materials. 

• For example, the number of sizes and size distributions of grains combined with colors, shapes and mineralogy is almost unlimited. It is this diversity in earth materials, combined with the ability to measure and observe the different kinds, which provides the forensic discriminating power.

The Five Soil Forming Factors • Parent Material

– Source of the soil

• Climate– How is the soil eroded

• Organisms– Plants or animals living in the soil

• Topography– Surrounding landscape

• Time– How long has the process evolved

Soil• The value of soil as evidence rests with its

prevalence at crime scenes and its transferability between the scene and the criminal.

• Most soils can be differentiated by their visual appearance.

• A side-by-side visual comparison of the color and texture of soil specimens is easy to perform and provides a criteria for distinguishing soils that originate from different locations.

Soil

• In many forensic laboratories, forensic geologists will characterize and compare the mineral content of soils.

Sifting

• Soil is often sifted through various mesh screens to separate it into its components.

Soil• Some crime laboratories

utilize density-gradient tubes to compare soils. – These tubes are typically

filled with layers of liquids that have different density values.

– When soil is added to the density-gradient tube, its particles will sink to the portion of the tube that has a density of equal value.

pH of Soil

• The pH of soil can help narrow its location

• pH is the acidity of the soil– pH < 7 is acidic– pH = 7 is neutral– pH > 7 is basic

Phosphorus Levels

• Another indicator of soil location is the level of phosphorus in the mixture.

Collection of Soil• Standard /reference soils are to be

collected at various intervals within a 100-yard radius of the crime scene, as well as the site of the crime, for comparison to the questioned soil.

• Soil found on the suspect, such as adhering to a shoe or garments, must not be removed.

• Instead, each object should be individually wrapped in paper, and transmitted to the laboratory.

Homework

• You and a partner collect 2 cups of dirt from a unique location in the immediate area. Package the dirt in a gallon zip lock bag. Take a 2 photos (overview and close up) of the area from which you collected the soil.

• Pg 416 22-27