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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. Forensic Geology. The legal application of earth and soil science
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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
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
Forensic Geologist Tools • Binocular microscopes • Petrographic microscopes • X-ray diffraction • Scanning electron microscopes • Microchemical analysis
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. • Hans Gross, a Austrian criminal investigator, wrote in his manual in 1893 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.”
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.
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
Soil • Formation • Livingmatter—plants, animals, microorganisms • Inorganic materials • Climate • Relief—slope and land form • Time
Profile Topsoil Subsoil Composition Sand Silt Clay Organic matter Soil
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
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
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
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
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.
Soil • The value of soil as evidence rests with its prevalence at crime scenes and its transferability between the scene and the criminal. • Most soils can be differentiated by their gross appearance. • A side-by-side visual comparison of the color and texture of soil specimens is easy to perform and provides a sensitive property for distinguishing soils that originate from different locations.
Collection of Soil • Standard /reference soils are to be collected at various intervals within a 100-yard radius of the crime scene, as well as the site of the crime, for comparison to the questioned soil. • Soil found on the suspect, such as adhering to a shoe or garments, must not be removed. • Instead, each object should be individually wrapped in paper, and transmitted to the laboratory.
Examination of Soil Throughout the examination of soil an observer must: • Look for trace evidence • Compare the physical and chemical properties of each sample to a control sample bsapp.com
Dry Samples & Pulverize • Dirt changes shade and color at different moisture levels • Make analysis after dirt has been dried in an oven or for extended time. • Dried dirt may clot bsapp.com
Gross Examination • Look at: • Color • Texture • Shapes • Foreign Objects bsapp.com
UV-Observations • Note the shape, size, number, and identity (if possible) of any material that fluoresces • Compare Samples bsapp.com
Soil Under UV Light bsapp.com
Mineral Under UV Normal Light UV Light bsapp.com
Microscopic Observation • Look at: • Color • Texture • Shapes • Foreign Objects bsapp.com
Steps for Microscopic Observation Place a thin layer of dirt on a slide Place only a small amount of sample on the slide at a time. Be sure the dirt is placed only in the center of the slide so as not to allow it to fall in the microscope. bsapp.com
Viewed with Naked Eye bsapp.com
Viewed with Microscopic x10 bsapp.com
Microscopic x40 (Cotton Fiber) bsapp.com
Microscopic x40 (Minerals) bsapp.com
Microscopic x40 (Organic Material) bsapp.com
Filtering the Soil • The premise is to size sort the material and use the mass (weight) of each particle range as a fingerprint for that soil type. • The range of particle sizes tells much about the history and formation processes for that soil. • Can re-examine if necessary
Final Comparison • Any and all foreign objects found should be investigated separately • If all previous comparisons are similar between two samples they likely originate from the same area • As final comparison density gradient columns may be utilized bsapp.com
Soil Analysis by Density • In many forensic laboratories, forensic geologists will characterize and compare the mineral content of soils. • Some crime laboratories utilize density-gradient tubes to compare soils.
Density Gradient Tubes • These tubes are typically filled with layers of liquids that have different density values. • When soil is added to the density-gradient tube, its particles will sink to the portion of the tube that has a density of equal value. • If the two samples are of the same origin, then they will produce nearly identical gradient tubes
Examples of Particles Suspended bsapp.com
Soil Analysis by pH There are two easy ways you can test soil pH. • A small sample of soil is collected, and then after a chemical reaction with a ‘universal’ pH indicator (one that has a different colour for every point on the pH range) the sample can be matched to a colour chart • You can add water to the soil and if the chemicals that are making it acidic or basic are soluble in water, then you can test the water to find out its pH.
Forensic Geologyin 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.
