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Chapter 13 Soil Analysis

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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. – PowerPoint PPT presentation

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Title: Chapter 13 Soil Analysis


1
Chapter 13Soil 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

2
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.

3
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

4
Forensic Geology History
  • 18871893Sir 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.
  • 1893An 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.

5
History
  • 1904Georg Popp, a German forensic scientist,
    presented the first example of earth materials
    used as evidence in a criminal case, the
    strangulation of Eva Disch.
  • 1910Edmond 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.

6
Soil
  • Definitionnaturally deposited materials that
    cover the earths surface and are capable of
    supporting plant growth
  • The Earth
  • 75oceans, seas and lakes
  • 15deserts, polar ice caps and mountains
  • 10suitable for agriculture

7
Soil Composition
  • C. Soil is part of the top layer of Earths
    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.

8
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.

9
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10
Chemistry of the Soil
  • The pH scale shows how acidic or basic something
    is.

11
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.

12
Soil Comparisons
  • May establish a relationship or link to the
    crime, the victim, or the suspect(s)
  • Physical propertiesdensity, magnetism, particle
    size, mineralogy
  • Chemical propertiespH, trace elements

13
Probative Valueof 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

14
IncreasingProbative Value
  • Rare or unusual minerals
  • Rocks
  • Fossils
  • Manufactured particles

15
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 identificationsize, density,
    color, luster, fracture, streak, or magnetism

16
Rocks
  • Aggregates of minerals
  • Types
  • Naturallike granite
  • Man-madelike concrete
  • Formation
  • Igneous
  • Sedimentary
  • Metamorphic

17
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

18
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 http//science.uniserve.edu.au/faces/milne/
    milne.html

19
Soil Evidence
  • Class characteristicsthe type of soil may have
    similar characteristics at the primary and/or
    secondary crime scene, on the suspect or on the
    victim
  • Individual characteristicsonly if the soil has
    an unusual or specialized ingredient such as
    pollen, seeds, vegetation, or fragments.

20
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).

21
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

22
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.)

23
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

24
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.

25
Mineral Composition of SandContinental and
Volcanic Sand
  • Note that the identifying feature of continental
    sand is quartz whereas there is no quartz in
    volcanic sand.

26
Mineral Composition of SandSkeletal 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.

27
Sand Types
  • Continental sandsformed from weathered
    continental rock, usually granite
  • Ocean floor sandsformed from volcanic material,
    usually basalt
  • Carbonate sandscomposed of various forms of
    calcium carbonate
  • Tufa sandsformed when calcium ions from
    underground springs precipitate with carbonate
    ions in the salt water of a salt lake

28
Sand EvidenceIn every grain of sand is a story
of earth. Rachel Carson
  • Class characteristicsthe type of sand may have
    similar characteristics to the primary and/or
    secondary crime scene, on the suspect or on the
    victim
  • Individual characteristicsonly if the sand has
    an unusual ingredient or contaminant.

29
Virtual Sand Lab
  • Take a look at other examples on the website
    from the Geology Department at Pasadena City
    College.
  • www.paccd.cc.ca.us/SAND/SandExrc.htm

30
Forensic Geologyin the News
  • A 9-year-olds 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 suspects 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 www.forensicgeology/sc
    ience.htm
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