0. “Life is hard. Then you die.
Chapter 13 Soil Analysis
“Life is hard. Then you die.
Then they throw dirt in your face. Then the worms eat you.
Be grateful it happens in that order.”
—David Gerrold, American science fiction writer

1. Kendall/Hunt Publishing Company
Introduction
Factors such as temperature, rainfall, and the chemicals and minerals in the soil influence the production of soil.
Soil from different locations can have different physical and chemical characteristics.
Because of this, soil analysis has been helpful in such things as linking suspects to crime scenes and locating burial sites.
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Forensic Geology
The legal application of earth and soil science
Characterization of earthen materials that have been transferred between objects or locations and the analysis of possible origin or sources
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3. Forensic Geology History
1887–1893—Sir Arthur Conan Doyle wrote about scientific ideas and techniques for solving crimes in his writings of Sherlock Holmes. This included information about soil and its composition which had never actually been used.
1893—An Austrian criminal investigator, Hans Gross, wrote that there should be a study of “dust, dirt on shoes and spots on cloth.” He observed, “Dirt on shoes can often tell us more about where the wearer of those shoes had last been than toilsome inquiries.”
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History
1904—Georg Popp, a German forensic scientist, presented the first example of earth materials used as evidence in a criminal case, the strangulation of Eva Disch.
1910—Edmond Locard, a forensic geologist, was most interested in the fact that dust was transferred from the crime scene to the criminal. This helped to establish his principle of transfer.
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Soil
Definition—naturally deposited materials that cover the earth’s surface and are capable of supporting plant growth
The Earth
75%—oceans, seas and lakes
15%—deserts, polar ice caps and mountains
10%—suitable for agriculture
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6. Kendall/Hunt Publishing Company
Soil Composition
C. Soil is part of the top layer of Earth’s crust.
It contains minerals, decaying organisms, water, and air in varying amounts.
Soil texture describes the size of the mineral particles that make up soil.
The 3 main grain sizes are sand, silt, and clay.
The 3 subcategories of soil are loam, peat, and chalk.
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7. Kendall/Hunt Publishing Company
Soil Profiles
Soils are formed in layers (horizons):
Humus, the O horizon, is made of decaying organic matter.
Topsoil, the A horizon, is a mixture of humus and minerals.
Sand and silt makes up the E horizon.
Subsoil, the B horizon, is made of clay and minerals.
Broken rock, the C horizon, has very little humus present.
Solid rock makes up the R horizon.
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Chemistry of the Soil
The pH scale shows how acidic or basic something is.
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Chemistry of the Soil
An important chemical property of soil is whether it is acidic or basic (alkaline).
Materials that make up a soil are not the only factors that affect its pH level.
Rainfall can change the pH value of a soil.
Pollution and fertilizer also can change the pH value of soil.
The pH value of a soil sample can help a forensic scientist match it to other samples.
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Soil Comparisons
May establish a relationship or link to the crime, the victim, or the suspect(s)
Physical properties—density, magnetism, particle size, mineralogy
Chemical properties—pH, trace elements
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12. Probative Value of Soil
Types of earth material are virtually unlimited. They have a wide distribution and change over short distances.
As a result, the statistical probability of a given sample having properties the same as another is very small
Evidential value of soil can be excellent
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13. Increasing Probative Value
Rare or unusual minerals
Rocks
Fossils
Manufactured particles
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Minerals
More than 2000 have been identified
Twenty or so are commonly found in soils; most soil samples contain only 3 to 5
Characteristics for identification—size, density, color, luster, fracture, streak, or magnetism
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Rocks
Aggregates of minerals
Types
Natural—like granite
Man-made—like concrete
Formation
Igneous
Sedimentary
Metamorphic
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Fossils
Remains of plants and animals
May help geologists to determine the age of rocks
Some are scarce and can be used to identify regions or locations
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Palynology
The study of pollen and spores
Important to know:
What is produced in a given area
The dispersal pattern
Variation in size and weight
For additional information about palynology visit:
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18. Kendall/Hunt Publishing Company
Soil Evidence
Class characteristics—the type of soil may have similar characteristics at the primary and/or secondary crime scene, on the suspect or on the victim
Individual characteristics—only if the soil has an unusual or specialized ingredient such as pollen, seeds, vegetation, or fragments.
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19. Kendall/Hunt Publishing Company
Soil Collection
In order to present credible evidence in
court, a chain of custody log is essential.
A person bags the evidence, marks it for identification, seals it, and signs it across the sealed edge (above, left).
It is signed over to a technician in a lab for analysis who opens it, but not on the sealed edge.
After analysis, the technician puts it back into the evidence bag, seals it in another bag, and signs the evidence log (above, right).
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20. Kendall/Hunt Publishing Company
Soil Examination
The presence of soil unique to a certain area can show that a suspect or victim must have been in that area.
Layers of soil or sand taken from shoes or the wheels of vehicles can show a suspect was present at a series of locations.
Explain how each of the following is useful in the examination of soil samples:
looking at samples macroscopically
X-ray diffraction
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Sand
Sand is the term applied to natural particles with a grain diameter between 1/16 mm and 2 mm.
Its color and contents are dependent upon the parent rock and surrounding plant and animal life.
(The photo on the right shows color differences in sand from six locations around the world.)
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22. Kendall/Hunt Publishing Company
Sand Characteristics
Composition is based on the material of the source; also gives the sand its color
Texture is determined by the way the source was transported
Shape
Grain size
Sorting
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23. Kendall/Hunt Publishing Company
Sand
The action of wind and water on rocks forms sand.
This may take millions of years.
Because water acts as a buffer, water produces sand more slowly than wind.
Wind-blown sand becomes rounded more quickly because the grains strike each other directly without a buffer.
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24. Mineral Composition of Sand —Continental and Volcanic Sand
Note that the identifying feature of continental sand is quartz; whereas there is no quartz in volcanic sand.
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25. Mineral Composition of Sand —Skeletal and Precipitate Sand
Skeletal sand gives off bubbles when mixed with an acid. Oolite formation is not a result of weathering but an example of depositions.
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Sand Types
Continental sands—formed from weathered continental rock, usually granite
Ocean floor sands—formed from volcanic material, usually basalt
Carbonate sands—composed of various forms of calcium carbonate
Tufa sands—formed when calcium ions from underground springs precipitate with carbonate ions in the salt water of a salt lake
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Sand Evidence “In every grain of sand is a story of earth.” —Rachel Carson
Class characteristics—the type of sand may have similar characteristics to the primary and/or secondary crime scene, on the suspect or on the victim
Individual characteristics—only if the sand has an unusual ingredient or contaminant.
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Virtual Sand Lab
Take a look at other examples on the website from the Geology Department at Pasadena City College.
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29. Forensic Geology in the News
A 9-year-old’s body was found in a wooded area along a river in Lincoln County, South Dakota. A forensic geologist collected soil samples from the fenders of a suspect’s truck and the area where the body was found. Both soils contained grains of a blue mineral that turned out to be gahnite, a rare mineral that had never been reported in South Dakota. As a result, the soil tied the suspect to the crime.
Check out other cases at:
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