Forensic Soil Examination Soils-4-1 Image: T. Loynachan

Story Time

Soil introduction Soil production is influenced by factors such as temperature, rainfall, and the chemicals and minerals present in the material from which it forms. Soil production is influenced by factors such as temperature, rainfall, and the chemicals and minerals present in the material from which it forms. –Made from the erosion of rock Example cases: Example cases: –Cattle rustlers stole herd of cattle from Missouri and took it to Montana –World War II Japanese tactics unveiled

What is soil? Top layer of the Earth’s crust where most plants grow. It contains the following: Top layer of the Earth’s crust where most plants grow. It contains the following: –Minerals –Decaying organisms –Water –Air Soil texture describes the size of the mineral particles that are in the soil. Soil texture describes the size of the mineral particles that are in the soil.

Six types of soil SoilFeelComposed ofLocationOtherPicture SandGrittyWeathered rock Deserts, beaches, riverbeds Large particles, loses water quickly ClayStickySmall particles sticking to one another VariousSmall particles, clumps, poor drainage SiltCrumbly, slippery like flour Medium-sized mineral particles Sediment in riverbeds Good drainage, easily farmed PeatCompressibleDecaying organic material Bogs, areas where decomposition is low Acidic, can retain water LoamLooseSand, silt and clay mixture VariousBest soil for agriculture Chalk_____Alkaline with mineral stones Below the top soil Poor for agriculture

Soil Profiles Soils form in layers (“horizons”) Soils form in layers (“horizons”) –Each horizon has charcteristic properties that differ from other horizons. –Soil in a given area will have a unique “profile” or sequence of layers O Horizon O Horizon –Made mostly of organic matter –Referred to as “humus” A Horizon A Horizon –Dark in color –“Topsoil” – mixture of humus and minerals. Where seeds sprout E Horizon E Horizon –Light in color –Mostly sand and silt –Where “leaching” occurs – water drips through the soil carrying away most minerals and clay originally present.

Soil Profiles continued B Horizon B Horizon –“subsoil” –Contains clay and mineral deposits that have leached out from layers above. C Horizon C Horizon –Made of partially broken-up rock. –Plant roots do not grow in this layer. –Very little humus found here R Horizon R Horizon –Present ONLY if solid rock layer is under all the others

Chemistry of the Soil (pH) pH is a measure of hydrogen ion (H + ) concentration ranging from 1-14 The lower the pH, the higher the hydrogen ion (H +) concentration --> acidic The higher the pH, the higher the hydroxyl (OH-) concentration --> alkaline (H+)=(OH-) pH=7, neutral

Why does pH matter? Hydrogen ions are involved in many chemical interactions so their presence is beneficial Too much hydrogen (acidic soil) decreases the plants ability to obtain nutrients from the soil. Alkaline soils (basic soil) have no excess hydrogen available for necessary chemical reactions

Soil Collection at a Crime Scene Collect ASAP – why? Collect ASAP – why? Collect surface “baseline” samples as well as samples that appear different or out of place – why? Collect surface “baseline” samples as well as samples that appear different or out of place – why? Collect at least 4 tablespoons from several locations – why? Collect at least 4 tablespoons from several locations – why? Sketch crime scene and note where soil samples were taken Sketch crime scene and note where soil samples were taken DO NOT remove soil on shoes, clothes, or tools (package these separately) – why? DO NOT remove soil on shoes, clothes, or tools (package these separately) – why? Carefully remove soil from vehicles and package separately Carefully remove soil from vehicles and package separately Collect additional soil samples from the four compass point (north, south, east, and west) within a few feet of the crime scene. Collect additional soil samples from the four compass point (north, south, east, and west) within a few feet of the crime scene.

Soil Examination Compare samples taken from suspect and crime to scene to samples taken from a known location. Compare samples taken from suspect and crime to scene to samples taken from a known location. –Can prove a suspect or victim was in the area –Can prove or disprove an alibi –Can prove cars were present in a specific location Compare size, shape, and color of soil. Compare size, shape, and color of soil. Look at soil type, plant and animal content, and particle size. Look at soil type, plant and animal content, and particle size.

Case Studies How can Layers of soil found on a suspect’s shoes show a sequence of where the suspect has traveled? How can Layers of soil found on a suspect’s shoes show a sequence of where the suspect has traveled? Andreas Schlicher (1908) Andreas Schlicher (1908) Enrique “Kiki” Camarena (1985) Enrique “Kiki” Camarena (1985) Janice Dobson (1995) Janice Dobson (1995)