1. Tracking Evidence
Dr. Walker

2. Vehicle Track Evidence
Objective:
To determine a match of tire tracks and/or vehicle make and model from tracks made in soft earth

3. Vehicle Track Evidence
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Vehicle Track Evidence
Basic Measurements
Wheelbase
Axle to axle distance

4. Vehicle Track Evidence
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Vehicle Track Evidence
Basic Measurements
Front Track Width
Distance between center points of front tires
Rear Track Width
Distance between center points of rear tires

5. Vehicle Track Evidence
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Vehicle Track Evidence
Basic Measurements
Tread design width
The measurement across the tread from one edge of the tread design to the other.
Turning diameter
Minimum distance that vehicle requires (curb to curb) to make a complete circle (360-degree turn).

6. Vehicle Track Evidence
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Vehicle Track Evidence
Basic Measurements
Tread design depth
The tread pattern depth on a tire (on site or from an impression.)
New tires (passenger vehicles) are 11/32” to 12/32”
Most mud or snow tires are 14/32” to 16/32”
Decreases over time due to wear

7. Vehicle Track Evidence
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Vehicle Track Evidence
Basic Measurements
Tire circumference
The full circumference of a tire.
Cuts, stains, or rocks may aid in obtaining this value
Actual measurements may be different than “real” tire values
Expansion/compression due to temperature changes within the tire.

8. Vehicle Track Evidence
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Vehicle Track Evidence
Tire Size
235/60R16
235 – Width of tire in millimeters
60 – Aspect Ratio (height of sidewall/width of tire)
16 – Diameter of tire in inches

9. Vehicle Track Evidence
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Vehicle Track Evidence
Tread patterns are often unique, and patented, for each manufacturer
Brand of tire can often be determined from the tread pattern.
As the vehicle is driven, the tires develop wear patterns.
Some wear faster on the front tires, some on the back.
There may be random cuts, nicks, or stones in the tread.
They all leave unique impressions at the crime scene that can be used to positively associate a vehicle with a crime.

10. Write bold
Forensic Geology
All forensic geology is designed to establish the degree of probability that a sample is derived from a given place
However, there are no mechanized ways to produce probability estimates. 

11. Components Of Physical Evidence
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Components Of Physical Evidence
The Soil Itself
The following may be included
Rocks
Minerals
Fossils

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Forensic Geology
Soil
Any disintegrated surface material, both natural and artificial, that lies on or near the earth’s surface.
Soil may include: Rock, minerals, vegetation, animal matter, glass, manufactured objects, asphalt, brick fragments, and paint chips.

13. Forensic Geology Soil Analysis
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Forensic Geology
Soil Analysis
Side-by-side visual comparison of color and texture when dry.
There are nearly 1100 distinguishable soil colors.

14. Forensic Geology Types of Soil Residual Soil
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Forensic Geology
Types of Soil
Residual Soil
Soil formed in place by the weathering of rocks
Transported Soil
Soil that has been moved by nature
By rivers or streams, to another location as mud, sand, or dust

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Soil Profile
Most biological (or organic) processes take place at layers near the surface (depth < 15”)
Soil Profile
Layering pattern of soil

16. Rocks Three Types Igneous melting of older rocks Metamorphic
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Rocks
Three Types
Igneous
melting of older rocks
Metamorphic
formed by pressure
Sedimentary
Formed by weathering

17. Rocks
Classified by size, shape, and the way the minerals fit together in the rock. 
Coarseness of the grain can be also classified, but the most defining feature is the prevalence of an index mineral comprising the vast majority of the rock
Petrology is the name for the science of the study of rocks.  

18. Minerals Minerals come in over 4000 varieties
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Minerals
Minerals come in over 4000 varieties
Only 200 are discussed in textbooks
Only 20 are considered common
Most samples may only have 4 or 5

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Minerals
Every mineral has an unique atomic structure with fixed physical and chemical properties
Classified as light or heavy based on specific gravity
Classified by color, luster, fracture, cleavage, streak 

20. Mineral Terms Luster Streak Fracture Cleavage
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Mineral Terms
Luster
Describes the way light is reflected from its surface
Streak
Color of the powder left behind when the mineral is rubbed against a hard, rough surface
Fracture
Rough, uneven breakage
Cleavage
Breaks along a smooth, definite line

21. Mineral Terms Hardness Ability of a mineral to resist being scratched
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Mineral Terms
Hardness
Ability of a mineral to resist being scratched
An object with a higher number will scratch an object with a lower number
Moh’s Hardness
Scale

22. Mineral Terms Light vs. Heavy Refers to specific gravity
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Light vs. Heavy
Refers to specific gravity
Specific gravity related to density
Indicates how many times more the mineral weighs compared to an equal amount of water
Description SG
Mineral Examples
very light
< 2
borax
light
gypsum, halite, selenite, ulexite
average
2 – 3
calcite,  dolomite, feldspar, muscovite mica, quartz, talc, turquoise,
above average / slightly heavy
3 - 4
biotite mica
heavy
4 – 5
almandine garnet, apatite, barite, celestite, chalcopyrite, fluorite
very heavy
5 – 10
 galena, hematite, magnetite, nickel-iron, pyrite
extremely heavy even for a metallic mineral
> 10
gold, silver
super heavy
20+
must be platinum!

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Fossils
Used by forensic geologists primarily to determine the age of rocks
Carbon dating used for age determination