Chapter 13 Soil Analysis

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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

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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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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.

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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.

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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

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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.

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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 propertiesdensity, magnetism, particle
  size, mineralogy
• Chemical propertiespH, trace elements

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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

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

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Rocks

• Aggregates of minerals
• Types
• Naturallike granite
• Man-madelike 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 http//science.uniserve.edu.au/faces/milne/
  milne.html

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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.

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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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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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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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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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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.

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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.

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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

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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.

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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

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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