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