Download Soil

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Soil Notes
EQ: How do forensic geologist
analyze soil evidence?
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What is soil?
 Soil
makes up the upper-most layer of the
earth’s crust.
 It
is composed of both organic and
inorganic materials.
Organic Materials
Decomposed
fragments of plants
and animals
Inorganic Materials
-Weathered rock
-Air
-Water
-Minerals
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What are physical characteristics
of soil?
 Size
 Density
 Temperature
 Water
 Color
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What is the chemical composition
of soil?
 Soil
is made up of :
 Oxygen - 46.7%
 Silicon - 27%
 Aluminum – 8.1%
 Iron 5%
 Lots
of plant minerals
are present –
 Calcium
 Magnesium
 Potassium
 Sodium
 Phosphorus
 Sulfur
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How do forensic scientists define
soil?
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There are 8 different “soil horizons,”
which are basically the different layers of
soil.

Forensic scientists deal with the
uppermost layer – Horizon O.

They analyze naturally occurring rocks,
minerals, as well as manufactured
objects.
 Glass, paint chips, asphalt, brick
fragments, cinders

These characteristics make soil unique
to a particular location.
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Why is soil so important in forensic
science?
 Soil
is considered to be valuable physical
evidence.
 The
dirt that accumulates at the bottom of
shoes contain minerals, fibers, etc. that may
link a perpetrator to the crime.
 Soil
helps biologists and mineralogists find out
the occupation, hobbies, and movement of the
criminal.
 Just
as soil helps confirm who the criminal is, it
can also be used to justify an alibi.
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How are soils differentiated and
distinguished by the eye?
 Soils
can be differentiated by their
appearance alone. The color and texture of
soil specimens make it much easier to
identify from where they came.
 There
are an estimated 1,100 different soil
colors.
 Since
soil is darker when wet, all
comparisons in the laboratory must be
done when samples are dry.
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How are soils differentiated and
distinguished using a microscope?
 Under
a low-power microscope
the presence of plant and animal
materials and artificial debris
can be seen.
 Under
a high-power microscope
minerals and rocks can be seen.
 Particle
size and shape can be
compared using a reflected light
microscope.
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How are the chemical properties of
soil distinguished?
 Forensic
scientists use xray diffraction to
compare the chemical
and mineralogical
composition of soil
 In
x-ray diffraction,
pulverized soil is
subjected to x-rays that
produce patterns that
indicate the structure of
minerals.
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What are minerals & why are they
important?
A
mineral is a naturally
occurring crystal.
 The
physical properties of
minerals, such as their color,
shape, density, and refractive
index help identify where
they came from.
 They
give geologists more
points of comparison.
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How are soil specimens
compared?
 Some
forensic scientists
use density-gradient tubes.
 Each tube is filled with
two layers of different
liquids. Each layer must
have a different density.
 The soil particles will sink
to the layer of the tube
that has an equal density.
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How easily are soil samples
matched?
 The
chance of matching soil samples is
dependent on the area. If the soil is
indistinguishable for miles, soil, as
evidence, will be limited.
 If
there are rare rocks or minerals, it is
much easier for a geologist to find a match.
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How is soil collected?

Soil is collected using a forensic vacuum or tape to lift the
particles.

Forensic scientists only need a tablespoon or two of soil
in order to run the tests they need.

When removing evidence from a place –
 It is important to take samples from the supposed alibi
location

When removing evidence from a person or object –
 The object/clothing should be individually wrapped in
paper and taken to the lab

When car accidents occur, the suspect’s car is checked
for soil under the fender and frame areas
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Vocabulary (in glossary)
Forensic Geology: The study of
evidence relating to minerals, soil,
petroleums, and other materials found
in the Earth used to answer questions
raised by the legal system
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Vocabulary (in glossary)
Density Gradient Tube: Equipment used
for measuring the distribution of
different particles in a soil sample by
establishing the point at which they are
suspended in a tube filled with layers
of liquid of different densities
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Density Mini Lesson
Density: The amount of matter in a given space
Density = Mass
Units: g/mL or g/cm3
Volume
* Fluids with the lowest density float, while fluids
with highest density sink.