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

Forensic Soil Forensic Soil ExaminationExamination

Soils-4-1

Image: T. Loynachan

Story TimeStory Time

Soil introductionSoil introduction

Soil production is influenced by factors Soil production is influenced by factors such as temperature, rainfall, and the such as temperature, rainfall, and the chemicals and minerals present in the chemicals and minerals present in the material from which it forms.material from which it forms.– Made from the erosion of rockMade from the erosion of rock

Example cases:Example cases:– Cattle rustlers stole herd of cattle from Cattle rustlers stole herd of cattle from

Missouri and took it to MontanaMissouri and took it to Montana– World War II Japanese tactics unveiled World War II Japanese tactics unveiled

What is soil?What is soil? Top layer of the Earth’s crust where Top layer of the Earth’s crust where

most plants grow. It contains the most plants grow. It contains the following:following:– MineralsMinerals– Decaying organismsDecaying organisms– WaterWater– AirAir

Soil texture describes the size of the Soil texture describes the size of the mineral particles that are in the soil.mineral particles that are in the soil.

Six types of soilSix types of soil

Soil Feel Composed of

Location Other Picture

Sand Gritty Weathered rock

Deserts, beaches, riverbeds

Large particles, loses water quickly

Clay Sticky Small particles sticking to one another

Various Small particles, clumps, poor drainage

Silt Crumbly, slippery like flour

Medium-sized mineral particles

Sediment in riverbeds

Good drainage, easily farmed

Peat Compressible

Decaying organic material

Bogs, areas where decomposition is low

Acidic, can retain water

Loam

Loose Sand, silt and clay mixture

Various Best soil for agriculture

Chalk

_____ Alkaline with mineral stones

Below the top soil

Poor for agriculture

Soil ProfilesSoil Profiles Soils form in layers (“horizons”)Soils form in layers (“horizons”)

– Each horizon has charcteristic properties that differ from other Each horizon has charcteristic properties that differ from other horizons. horizons.

– Soil in a given area will have a unique “profile” or sequence of Soil in a given area will have a unique “profile” or sequence of layerslayers

O Horizon O Horizon – Made mostly of organic matterMade mostly of organic matter– Referred to as “humus”Referred to as “humus”

A HorizonA Horizon– Dark in colorDark in color– ““Topsoil” – mixture of humus and minerals. Where seeds Topsoil” – mixture of humus and minerals. Where seeds

sproutsprout E HorizonE Horizon

– Light in colorLight in color– Mostly sand and siltMostly sand and silt– Where “leaching” occurs – water drips through the soil Where “leaching” occurs – water drips through the soil

carrying away most minerals and clay originally present.carrying away most minerals and clay originally present.

Soil Profiles continuedSoil Profiles continued

B HorizonB Horizon– ““subsoil”subsoil”– Contains clay and mineral deposits that have leached Contains clay and mineral deposits that have leached

out from layers above.out from layers above. C HorizonC Horizon

– Made of partially broken-up rock.Made of partially broken-up rock.– Plant roots do not grow in this layer.Plant roots do not grow in this layer.– Very little humus found hereVery little humus found here

R HorizonR Horizon– Present ONLY if solid rock layer is under all the othersPresent ONLY if solid rock layer is under all the others

Chemistry of the Soil (pH)Chemistry of the Soil (pH)

pH is a measure of hydrogen ion (HpH is a measure of hydrogen ion (H++) ) concentration ranging from 1-14concentration ranging from 1-14

The lower the pH, the higher the The lower the pH, the higher the hydrogen ion (Hhydrogen ion (H+)+) concentration --> concentration --> acidicacidic

The higher the pH, the higher the The higher the pH, the higher the hydroxyl (OH-) concentration --> hydroxyl (OH-) concentration --> alkalinealkaline

(H+)=(OH-) pH=7, neutral(H+)=(OH-) pH=7, neutral

Why does pH matter?Why does pH matter?

Hydrogen ions are involved in many Hydrogen ions are involved in many chemical interactions so their chemical interactions so their presence is beneficialpresence is beneficial

Too much hydrogen (acidic soil) Too much hydrogen (acidic soil) decreases the plants ability to obtain decreases the plants ability to obtain nutrients from the soil.nutrients from the soil.

Alkaline soils (basic soil) have no Alkaline soils (basic soil) have no excess hydrogen available for excess hydrogen available for necessary chemical reactionsnecessary chemical reactions

Soil Collection at a Crime Soil Collection at a Crime SceneScene

Collect ASAP – why?Collect ASAP – why? Collect surface “baseline” samples as well as samples that Collect surface “baseline” samples as well as samples that

appear different or out of place – why?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 Sketch crime scene and note where soil samples were

takentaken DO NOT remove soil on shoes, clothes, or tools (package DO NOT remove soil on shoes, clothes, or tools (package

these separately) – why?these separately) – why? Carefully remove soil from vehicles and package separatelyCarefully remove soil from vehicles and package separately Collect additional soil samples from the four compass point Collect additional soil samples from the four compass point

(north, south, east, and west) within a few feet of the crime (north, south, east, and west) within a few feet of the crime scene.scene.

Soil ExaminationSoil Examination

Compare samples taken from suspect and crime Compare samples taken from suspect and crime to scene to samples taken from a known location.to scene to samples taken from a known location.– Can prove a suspect or victim was in the areaCan prove a suspect or victim was in the area– Can prove or disprove an alibiCan prove or disprove an alibi– Can prove cars were present in a specific locationCan 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 Look at soil type, plant and animal content, and

particle size. particle size.

Case StudiesCase Studies How can Layers of soil found on a How can Layers of soil found on a

suspect’s shoes show a sequence of suspect’s shoes show a sequence of where the suspect has traveled?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)