Cases involving Soil Evidence 1

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