If you happen to be a big fan of crime shows like CSI or Forensic Files, you may have observed members of the lab team analyse soil sample that were found at the scene of the crime. These samples were usually taken from the victim’s shoes and were not found anywhere in the vicinity of the crime scene. Alternatively, these samples could also be taken from tire treads of cars that are suspected to have been used in the crime.

Soil is more than just plain dirt. It is a mixture of several elements including minerals, plants, animal mater and even small particles of synthetic products such as glass, paint, asphalt, cement, and others. The components of soil are not uniform and vary from one place to another even within the same state or country. For example, soil found on the beach in Ocean City, Maryland has different components from soil found on the beach in Myrtle Beach, South Carolina.

The first step in the analysis of soil samples is visually and microscopically examining the soil to determine the acidity, consistency, colour, and mineral content. In the next step, the forensic scientist tries to uncover foreign particles such as plant matter like leaves and roots, or animal matter like hair, teeth, and nails. Discovering such aspects allows scientists to place the suspect or victim at a particular location. For example, if a suspect’s car has some quantity of beachfront sandy soil on its carpets, his statement that he was never at the beach where the crime may have occurred can be refuted. Similarly, if one was to find horse dung in the soil sample, it can be assumed that it came from a horse farm and not from the suspect’s backyard as he stated.

In depth forensic chemical analysis can also reveal whether two soil samples possess the same chemical properties. The criminalist can use a method known as x-ray diffraction to examine, analyse, and compare the mineral components of different soil samples. Another method that can be used to find individual components of a soil sample is gas chromatography/mass spectroscopy (GC/MS).

 

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Yet another laboratory technique is the differential thermal analysis. The premise behind this procedure is that soil releases as well as absorbs heat from the atmosphere at different rates. In this particular analysis, a soil sample is heated and the points at which the soil breaks down, melts, or boils is recorded. These results are then compared to the thermal properties of other soil samples which are analysed similarly. This comparison reveals whether the properties of these samples are consistent enough for the samples to be considered a match.

Forensic laboratory science is a powerful tool especially when solving criminal cases like hose of murder. The next time you watch your favourite crime show, you’ll have a pretty good understanding of why soil samples play such an important role during the investigation of the crime.