03.04 Soil and Impressions
For the forensic scientist, soil is more than dirt. Soil is thought of as surface material from the earth, both natural and artificial. In other words, soil includes not only dirt but also rocks, animal material, and vegetation that lie near the surface of the ground. In addition, it may include pieces of glass, fragments of brick or stone, and pieces of asphalt. The combination of things in the soil may help link a suspect to the crime scene if the soil is somehow transferred to the suspect on his or her shoes or clothing, for example. Comparing soil from a crime scene with a sample of soil that may have transferred to a suspect may allow forensic scientists to create a link between the crime scene and the suspect. Many soils can be distinguished from other samples by their color and texture. While visually looking at the soil samples can show differences, it is important to note that soil will look darker when it is wet so color comparisons should be done when the soil samples are dry. Microscopic analysis can also reveal the presence or absence of any vegetation or animal material. Artificial materials like glass particles are also more easily seen under a microscope. A forensic geologist may use a high-powered microscope to examine the sample for rock and mineral materials that can further tell investigators whether samples show similarity to each other. Due to the wide range of materials that can be found in soil, there are many aspects or points that forensic geologists can compare for two soil samples. The more similarities in these points, the greater likelihood that the two soil samples come from the same place. However, the range of soil that meets these similarities has to be taken into consideration. For example, if the soil around a crime scene is similar for a mile around the crime scene, it is less useful than if the soil is only similar within the crime scene or in a particular spot in the crime scene. Rare...
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