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Chapter 12 Soil Examination

GMA Manson Murders

Charles Manson- Dr. Baden

Decomposition

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Introduction 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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History of Forensic Soil History of Forensic Soil Examination Examination

Dr. Hans Gross is believed to be one of the first to recognize the importance of physical evidence.

His Criminal Investigation, written in 1893, had ground breaking material in this science.

Georg Popp is credited with being the first to use soil evidence to solve a crime.

He linked soil samples found on a suspect with samples found at the crime scene.

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Soil Composition

*Any disintegrated surface material, both natural and artificial that lies on or near the earth’s surface

Rocks –combo of minerals (40 common minerals can be found)

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Soil Composition Soil Composition

Soil is part of the top layer of Earth’s 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 (don’t copy)

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

– 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.

* Beside pH , other chemical tests can be run –like reactions with certain chemicals (ex. HCl- Carbonates bubbles)

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Sand 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 Sand

Sand from different locations contains different combinations of minerals.

*The most common mineral found in sand is quartz.

*Other than quartz, mineral content of sand can include: – feldspars – micas – iron compounds

*Sand also can be made of organic material such as coral and seashells.

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Mineral Composition of Sand—*Continental and Volcanic Sand

*Note that the identifying feature of continental sand is quartz; whereas there is no quartz in volcanic sand but has volcanic ash

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Mineral Composition of Sand—*Skeletal and Precipitate Sand

*Skeletal sand (shells) gives off bubbles when mixed with an acid. Oolite or Precipitate (CaCO3)formation is not a result of weathering but an example of depositions.

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Other soil types (in book)

Clay Small particles, poor drainage

Sticky feel

Silt Medium sized particles, good drainage, easily farmed

Crumbly, slippery like flour

Peat Decaying organic material, retains water

Compressible

Loam Sand,silt, clay mix, best for ag.

Loose

Chalk Below top soil, bad for ag.

Basic soil w/mineral stones

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Soil Soil Collection (don’t copy)Collection (don’t copy)

In order to present credible evidence in court, a chain of custody log is essential.

1. A person bags the evidence, marks it for identification, seals it, and signs it across the sealed edge (above, left).

2. It is signed over to a technician in a lab for analysis who opens it, but not on the sealed edge.

3. 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 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.

*Soil is class evidence

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Testing Soil

Done by forensic geologist No two places have precisely the same soil *Test:

– side by side comparison (macroscopic)– Microscope (both low and high power)– Look at color (1100 colors possible),

fluorescence, pH, chemical reactions– Find density with density-gradient tube

FBI old video

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