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Soil

+Soil Questions

(1) What is soil?

(2) What are the physical characteristics of soil?

(3) What is the chemical composition of soil?

(4) How do forensic scientists define soil?

(5) Why is soil so important in forensic science?

(6) How are soils differentiated and distinguished by the eye?

(7) What are minerals and why are they important?

(8) How easily are soil samples matched?

(9) How is soil collected?

+What is soil?Soil makes up the upper-most layer of

the earth’s crust.

It is composed of both organic and inorganic materials.

Organic Materials Inorganic Materials

Decomposed fragments of plants and animals

-Weathered rock-Air-Water-Minerals

+What are physical characteristics of soil?

Size

Density

Temperature

Water

Color

+What is the chemical composition of soil?Soil is made up of

:Oxygen - 46.7%Silicon - 27%Aluminum –

8.1%Iron 5%

Lots of plant minerals are present – CalciumMagnesiumPotassiumSodiumPhosphorusSulfur

+How do forensic scientists define soil? There are 8 different “soil horizons,”

which are basically the different layers of soil.

Forensic scientists deal with the uppermost layer – Horizon O.

They analyze naturally occurring rocks, minerals, as well as manufactured objects. Glass, paint chips, asphalt, brick

fragments, cinders

These characteristics make soil unique to a particular location.

+Why is soil so important in forensic science?

Soil is considered to be valuable physical evidence.

The dirt that accumulates at the bottom of shoes contain minerals, fibers, etc. that may link a perpetrator to the crime.

Soil helps biologists and mineralogists find out the occupation, hobbies, and movement of the criminal.

Just as soil helps confirm who the criminal is, it can also be used to justify an alibi.

+How are soils differentiated and distinguished by the eye?

Soils can be differentiated by their appearance alone. The color and texture of soil specimens make it much easier to identify from where they came.

There are an estimated 1,100 different soil colors.

Since soil is darker when wet, all comparisons in the laboratory must be done when samples are dry.

+How are soils differentiated and distinguished using a microscope? Under a low-power

microscope the presence of plant and animal materials and artificial debris can be seen.

Under a high-power microscope minerals and rocks can be seen.

Particle size and shape can be compared using a reflected light microscope.

+How are the chemical properties of soil distinguished?

Forensic scientists use x-ray diffraction to compare the chemical and mineralogical composition of soil

In x-ray diffraction, pulverized soil is subjected to x-rays that produce patterns that indicate the structure of minerals.

+What are minerals & why are they important?

A mineral is a naturally occurring crystal.

The physical properties of minerals, such as their color, shape, density, and refractive index help identify where they came from.

They give geologists more points of comparison.

+How are soil specimens compared?

Some forensic scientists use density-gradient tubes. Each tube is filled with

two layers of different liquids. Each layer must have a different density.

The soil particles will sink to the layer of the tube that has an equal density.

+How easily are soil samples matched?

The chance of matching soil samples is dependent on the area. If the soil is indistinguishable for miles, soil, as evidence, will be limited.

If there are rare rocks or minerals, it is much easier for a geologist to find a match.

+How is soil collected?

Soil is collected using a forensic vacuum or tape to lift the particles.

Forensic scientists only need a tablespoon or two of soil in order to run the tests they need.

When removing evidence from a place – It is important to take samples from the supposed

alibi location

When removing evidence from a person or object – The object/clothing should be individually

wrapped in paper and taken to the lab

When car accidents occur, the suspect’s car is checked for soil under the fender and frame areas