In order to
properly understand how Forensic Soil Analysis is performed one must understand
what soil is. Soil is a layer of earth in which plants grow, a
black or dark brown material typically consisting of a mixture of organic
remains, clay, and rock particles (oxforddictionaries.com, 2017). Scientists
describe soil as being made up of differently sized particles like sand, salt,
and clay (Tibbett, M., & Carter, D. O. 2008). Soil contains a complex
biological, chemical, physical, and mineralogical properties that always change
as time goes on (Tibbett, M., & Carter, D. O. 2008). Forensic Soil Analysis
uses soil sciences and other disciplines to aid in a criminal investigation
(crime museum, 2017). Soil in a way resembles fingerprints because of the fact
that each sort of soil that exists has distinguished properties that are like
identification marks (crime museum, 2017). This implies the origins of the dirt
can be recognized or identified to link to crime scenes (crime museum, 2017).
For instance, mud stuck under a tennis shoe of a criminal can be followed back
to a particular mud found along an area where a murder casualty was found
(crime museum, 2017). The largest part of soil cases includes impressions from
footprints or tire tracks that have been left in the dirt of crime scenes (crime
stated before soil has many different properties that make them unique into
narrowing down variables in a crime scene.
The three main unique properties of soil are as follows:
which is the original solid particles that could be in the form of a grain of
rock that breaks off of the larger parent material (crime museum, 2017).
Soils can develop on these sediments due to physical and chemical alteration (crime
Color, which indicates its history
as well as the compounds present in the soil (crime museum, 2017).
which indicates whether a soil is composed of a single grain particle or not.
This is determined by the presence of clumps that are formed due to cementing
agents such as calcium carbonate attracting the soil particles so that they
adhere to each other (crime museum, 2017).
Over time criminals have
become smart and well-aware that they need to hide and cover their trails like fingerprints when
committing a crime (study.com, 2017). Some are even adept at trying to destroy
DNA evidence from a crime scene (study.com, 2017). But rarely does the news
report that soil-based evidence was destroyed or pre-empted by a criminal
(study.com, 2017). Most likely because not long ago, no one, not even law
enforcement, thought much of using soil as a means of criminal investigations
(study.com, 2017). But now forensic soil analysis and evidence can help find
bodies, disprove alibis, and help figure out where an important piece of
evidence came from (study.com, 2017).
The way soil is collected, preserved, and tested is one of the
main contributions Forensic soil analysis brings to the success of crime labs
in the field (study.com, 2017). Before any soil can be tested or
analyzed it must first be collected, and then properly contained for
preservation for later analysis (study.com, 2017).
Criminal investigators will collect control samples, which are samples of soil, rock, or sediment that
are taken at a known date, time, and location (study.com, 2017).
Such control samples are then compared to questioned soil samples, soil found on objects of interest, like
shoes or tools (study.com, 2017). Soil
samples are collected in different ways depending on where it is being
collected from (crime museum, 2017). If samples are
being collected indoors or from a vehicle vacuuming is generally used (crime
museum, 2017). If the sample is outdoors it’s collected by
placing a teaspoon of soil into a plastic vial (crime museum, 2017). When found on a tool, it is wrapped in plastic and then
sent to the lab for testing (crime museum, 2017). When soil samples are collected off of a it takes more work
and care so that the evidence doesn’t get contaminated (crime museum,
2017). When collecting samples from a body, samples
should be taken at regular intervals and a different spoon should be used each
time (crime museum, 2017).
The collected control samples should be
placed into rigid, airtight and watertight plastic containers (study.com, 2017). Paper bags and polythene
bags are not always adequate when storing soil evidence due to risk of
punctures and tears in some kinds of samples (study.com, 2017). Metal containers add contaminants to samples
and should are avoided when obtaining soil (study.com, 2017). Glass jars can be used in some cases where some
soil samples may react with plastic, but normally their usage is avoided since
they may break (study.com, 2017).
When glass jars used the lids on them would be lined with non-reactive material
(study.com, 2017). All Criminal
Investigators/Forensic Soil Analyst label in the field using pre-determined
code by taking supporting information such as photographs of the sampling
location, as well as notes about the location and condition of recovery (study.com, 2017).
Once soil samples are obtained they’ll be sent to
the laboratory. At the laboratory samples are separated by the victim and the
suspect (crime museum, 2017). To examine the samples an examiner uses a
microscopic analysis to do testing on the mineral content. Another test that
analyst do to identify the origin of soil is a density test. The density test
consists of adding liquid to two glass tubes (crime museum, 2017).
The liquid in both tubes is the same, but the rations are different (crime
museum, 2017). This represents two different densities (crime
museum, 2017). The soil sample is added to both liquid samples (crime
museum, 2017). When the soil samples are suspended in the liquid the separation
of the bands are analyzed to reveal the contents of the soil (crime
museum, 2017). Heat tests are also used to test soil reaction and
electron microscopes can be used to examine the structure of the minerals in
the soil (crime museum, 2017). During examination, an examiner will find that
some soil samples contain biological evidence such as saliva, semen or blood (crime
museum, 2017). If biological evidence is found in the sample the
whole soil sample is sent to the laboratory for further testing (crime
In conclusion the foundations of Forensic Science reaches
back hundreds of years, and history records various cases in which people
firmly observed evidence and connected basic scientific principles to solve
crimes. With the steady advance of forensic science technologies during
the twentieth century various fields Soil Analysis have impacted the Criminal
Justice system in a positive to way to aid in suspect apprehension. Forensic
Soil Analysis may not be the center of
both forensic investigation of ongoing criminal cases and research but, new
techniques are being discovered every day to aid investigators in the future.