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Forensic Science: Fundamentals & Investigations, 2e Chapter 13 1 All rights Reserved Cengage/NGL/South-Western © 2016
Forensic Science: Fundamentals & Investigations, 2e
Chapter 13 1 All rights Reserved
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Forensic Science: Fundamentals & Investigations, 2e
Chapter 13
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Chapter 13 Soil Examination By the end of this chapter you will be able to:
13.1 Describe the distinguishing characteristics and compositions of different soils.
13.2 Compare and contrast the different soil layers found in a soil profile.
13.3 Compare and contrast the four different sources of sand.
13.4 Analyze soils using macroscopic and microscopic examination, as well as chemical and physical testing.
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Chapter 13 Soil Examination By the end of this chapter you will be able to:
13.5 Describe the effects of different physical and chemical compositions of soils on the decomposition of a corpse.
13.6 Explain how soil analysis can link a suspect, victim, tool, or other evidence item to a crime scene.
13.7 Explain how soil profiles and differences in the soil surface can be used to locate a gravesite.
13.8 Summarize how to collect and document soil evidence.
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o clay
o geology
o humus
o mineral
o sand
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Chapter 13
Vocabulary
o sediment
o silt
o soil
o soil profile
o weathering
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Introduction
o Soil from different locations has different physical and chemical characteristics that are useful to forensic scientists.
o Cow manure analysis enabled authorities to convict cattle rustlers who stole a herd of cattle from Missouri.
o During World War II, sand analysis enabled American forces to determine the geographical origin of bombs that were sent to America in hydrogen-filled balloons.
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History of Forensic Soil Examination
o During the late 1800s, Sir Arthur Conan Doyle wrote about the use of geology in the investigation of crime in his Sherlock Holmes novels.
o In 1893, Dr. Hans Gross was one of the first investigators to apply science to crime investigation.
o In 1904, Georg Popp was one of the first forensic scientists to use soil evidence to solve a crime.
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Soil Composition
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Soil Profiles
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Soil Profiles (continued)
o Humans disturb soil layers when a body is buried.
• Topsoil and humus may be lower in the profile.
• Subsoil and rocks may be on the surface.
o When a gravesite is filled after a burial, the soil profile is changed.
o Databases of soil profiles are available to forensic investigators who need to compare the soil profile of the evidence to find locations in which to search.
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Sand
o Weathering is the formation of sand based on the action of wind and water on rocks.
o Sand grains range in size from 0.05 mm to 2 mm in diameter.
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Sand (continued)
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Aging and Rounding of Sand
o Sand grains are classified as immature, young, old, or mature.
o Immature sand contains a large portion of clay, and the grains have a high percentage of fragments.
o Mature sand does not contain clay and has fewer jagged edges.
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Mineral Composition of Sand
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Continental Sand
o Continental Sand is composed mostly of:
• Quartz
• Mica
• Feldspar
• Dark colored minerals like hornblende and magnetite
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Volcanic Sand
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o Volcanic sand is usually dark as a result of the presence of black basalt or green olivine.
o This sand comes from mid-ocean volcanoes or hot-spot volcanoes.
o It is very young sand.
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Skeletal (Biogenic) Sand
o Skeletal sand is made of the remains of marine organisms.
o It takes less time to form than other types of sand.
o It occurs only in tropical regions.
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Precipitate Sand
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o When water evaporates, minerals come out of the water solution.
o Deposition is the depositing of layers of material.
o Oolitic sand can be found in various places including the Great Salt Lake in Utah.
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Soil Chemistry
o When a body is buried directly in soil, it affects the soil chemistry in a complex series of ways.
o A cadaver decomposition island (CDI) is formed by the concentrated decomposition products emitted from the body.
• Vegetation is initially killed.
o As decomposition continues, soil quality improves rapidly.
• A small area containing different plants than the rest of the vicinity arises.
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Soil Chemistry (continued)
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Soil Evidence
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o Proper procedures for soil evidence include the following:
1. Photograph and document the crime scene.
2. Sketch the evidence as the locations and types of evidence are noted.
3. Collect at least four tablespoons of material from multiple locations at the crime scene.
4. Collect soil samples from beyond the crime scene.
5. Document, package, and label all samples according to guidelines in Chapter 2.
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Soil Evidence Analysis
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o X-ray diffraction is a method of determining the mineral composition of soil.
o Each mineral and chemical produces a unique pattern.
o The reliability of soil sample evidence continues to be questioned by the courts.
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Finding Gravesites
o Citing possible gravesites is best done when the sun is low and shadows are easier to see.
o Gravesites may cast an unusual shadow for a terrain.
o A buried, decomposing body is affected by:
• Burial depth and rock content
• Soil moisture and underground water
• Soil texture
• Soil pH
• Oxygen level
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o Soil evidence from crime scenes, victims, and suspects has helped to solve crimes since the late 1800s.
o There are three textures of soil, based on particle size: clay, silt, and sand. Most soils are a mixture of minerals, decaying organic matter, water, and air.
o Soil forms layers called horizons and makes up a profile unique to an area. An altered soil profile can indicate the soil was disturbed and can be of forensic value.
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Summary
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o The pH of soil influences the type of microorganisms and plants living in it. Soil pH also affects how a body decomposes.
o Sand is formed when weathering breaks up rock into small grains ranging from 0.05 millimeters to 2 millimeters in diameter.
o There are four main sources of sand: continental sand, volcanic sand, skeletal sand, and precipitate sand.
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Summary (continued)
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o There are special procedures crime-scene investigators must follow when photographing, documenting, and collecting soil evidence.
o Understanding soil and sand helps forensic investigators link a person or object to a crime scene, locate a potential gravesite, and better understand the speed and manner in which a body decomposes.
o Soil analysis can involve macroscopic and microscopic examination, chemical testing, exposure to ultraviolet radiation, and X-ray diffraction analysis.
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Summary (continued)
