Title: Down and Dirty: The Formation of Soils
1Down and Dirty The Formation of Soils
2 Earths external processes
- Weathering the physical breakdown
(disintegration) and chemical alteration
(decomposition) or rock at or near Earths
surface - Erosion the physical removal of material by
mobile agents such as water, wind, ice, or gravity
3Weathering
- Two types of weathering
- Mechanical weathering breaking of rocks into
smaller pieces - Four types of mechanical weathering
- Frost wedging alternate freezing and thawing of
water in fractures and cracks promotes the
disintegration of rocks
4 Weathering
- Mechanical Weathering continued
- Unloading exfoliation of igneous and
metamorphic rocks at the Earths surface due to a
reduction in confining pressure - Thermal expansion alternate expansion and
contraction due to heating and cooling - Biological activity disintegration resulting
from plants and animals
5Weathering
- Chemical Weathering
- Breaks down rock components and internal
structures of minerals - Most important agent involved in chemical
weathering is water (responsible for transport of
ions and molecules involved in chemical processes)
6Weathering
- Major processes of chemical weathering
- Dissolution
- Aided by small amounts of acid in the water
- Soluble ions are retained in the underground
water supply - Oxidation
- Any chemical reaction in which a compound or
radical loses electrons
7Weathering
- Major processes of chemical weathering
- Oxidation continued
- Important in decomposing ferromagnesian minerals
- Hydrolysis
- The reaction of any substance with water
- Hydrogen ion attacks and replaces other positive
ions
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9Weathering
- Alterations caused by chemical weathering
- Decomposition of unstable minerals
- Generation or retention of materials that are
stable - Physical changes such as the rounding of corners
or edges
10Weathering
- Rates of weathering
- Advanced mechanical weathering aids chemical
weathering by increasing the surface area - Others factors affecting weathering
- Rock characteristics
- Rocks containing calcite (marble and limestone)
readily dissolve in weakly acidic solutions
11granite
limestone
An obvious example of how weathering differs
with different mineral solubilities
12 Increase in surface area by mechanical
weathering
13Weathering
- Others factors affecting weathering
- Rock characteristics continued
- Silicate minerals weather in the same order as
their order of crystallization
14Others factors affecting weathering, contd
- Climate
- Temperature and moisture are the most crucial
factors - Chemical weathering is most effective in areas of
warm, moist climates
15Weathering
- Differential weathering
- Masses of rock do not weather uniformly due to
regional and local factors - Results in many unusual and spectacular rock
formations and landforms
16 Differential weathering controlled by jointing
patterns
17 Joint-controlled weathering in igneous
rocks
18Soil
- Soil is a combination of mineral and organic
mater, water, and air - That portion of the regolith (rock and mineral
fragments produced by weathering) that supports
the growth of plants
19 Typical components in a soil that yields good
plant growth
20Soil
- Factors controlling soil formation
- Parent material
- Residual soil parent material is the underlying
bedrock - Transported soil forms in place on parent
material that has been carried from elsewhere and
deposited
21Soil
- Factors controlling soil formation
- Time
- Important in all geologic processes
- Amount of time for soil formation varies for
different soils depending on geologic and
climatic conditions - Climate
- Most influential control of soil formation
- Key factors are temperature and precipitation
22Soil
- Factors controlling soil formation
- Plants and animals
- Organisms influence the soils physical and
chemical properties - Also furnish organic matter to the soil
- Slope
- Steep slopes often have poorly developed soils
- Optimum terrain is a flat-to-undulating upland
surface
23 Variations in soil development due to
topography
24Soil
- The soil profile
- Soil forming processes operate from the surface
downward - Vertical differences are called horizons zones
or layers of soil
25 Soil
- The soil profile
- O horizon organic matter
- A horizon organic and mineral matter
- High biological activity
- Together the O and A horizons make up the topsoil
- E horizon little organic matter
- Zone of eluviation and leaching
26 Soil
- The soil profile
- B horizon zone of accumulation
- C horizon partially altered parent material
- The O, A, E, and B horizons together are called
the solum, or true soil
27An idealized soil profile
28A soil profile showing different horizons
O
A
B
C
29 Soil
- Soil types
- The characteristics of each soil type primarily
depend on the prevailing climatic conditions - Three very generic soil types
- Pedalfer, Pedocal, Laterite
30 Soil
- Three very generic soil types
- Pedalfer
- Best developed under forest vegetation
- Accumulation of iron oxides and Al-rich clays in
the B horizon - Pedocal
- Associated with dry grasslands and brush
vegetation - High accumulations of calcium carbonate
- Laterite
- Hot and wet tropical climates
- Intense chemical weathering
31Significance of Soil to Forensics
Although soils can be grouped together in various
categories according to characteristics, no two
soils are truly identical. This is partly a
function of the fact that no two parent materials
(e.g. rocks) are truly identical. Also, the
amounts and types of organic material contained
in soils differ according to climate and
vegetation type
32To trace the transfer patterns or ultimate source
areas of particular soils, forensic geologists
focus on the unusual, rather than the
usual. Features unique to soil of a particular
area can include distinctive minerals, texture,
and colour Soils are the most common materials
used in forensic geology because of their
dominance on the Earths surface (soils are most
likely to be picked up and transferred), and
their diverse characteristics. In some cases,
the concept of superposition is also useful
33A famous example
34Coors Case
Adolph Coors III (age 44, grandson Adolph Coors
I, the founder of Coors brewery), disappeared on
the morning of February 9, 1960 near Morrison,
Colorado (near Denver).
Denver
Morrison
35Coors car was later found with the motor still
running Coors glasses, hat, and spots of blood
were found at the scene, suggesting murder of the
victim and removal of the body.
36 A car belonging to a suspect (Joseph Corbett,
Jr.) was discovered February 17, burning in a
garbage dump in Atlantic City, New Jersey Was
there a connection ?
37Soil samples obtained from the fender of the car
showed four distinct layers
38Deposited first
Outermost layer (deposited last) matched soil
sampled at the entrance of the dump The three
inner layers were obviously different than the
last-deposited layer and had a mineralogy with
broad similarities to soils from the Rocky
Mountain Front west of Denver, Colorado
Layer 1
Layer 2
Layer 3
Layer 4 (dump site soil)
Fender Surface
Colorado Soil ?
Deposited last
39With hopes of locating the victim, investigators
collected over 350 samples from Rocky Mountain
Front, comparing these samples with soil on
suspects car. Before analyses were completed,
Coors body was found about 43 km south of
Denver. Sept. 12-14, 1960 Most of Coors
body recovered Sept. 15, 1960 Coors skull
located
40Layer 1
Layer 2
Further soil comparisons indicated similarities
between layer 3 on fender and soil where body was
found (south of Denver) material included
distinctive pink feldspar from Pikes Peak
granite)
Layer 3 (body site)
Layer 4 (dump site soil)
Fender Surface
Colorado Soil ?
41Deposited first
Further soil comparisons indicated similarities
between layer 2 on fender and soil from Dakota
Hogback where Coors ranch was located (material
included grains derived from sandstone, gray,
green and maroon shales, and traces of limestone)
Layer 1
Layer 3 (body site)
Layer 2 ( Coors ranch)
Layer 4 (dump site soil)
Colorado soil ?
Fender Surface
42Deposited first
The origin of layer 1 was inconclusive, but was
determined to have been sourced from somewhere in
the Denver area (grains diagnostic of weathered
Front Range granites in Denver area)
Layer 1
Layer 3 (body site)
Layer 2 ( Coors ranch)
Layer 4 (dump site soil)
Fender Surface
Denver-area soil ?
43Some additional evidence that surfaces in the
investigation
March, 1951 Corbett pleads guilty to
second-degree murder in San Rafael County,
California -sentenced to a term of five years to
life -eventually jailed at California Institution
for Men, Chino, California. August 1, 1995
Corbett escapes from California Institution of
Men, Chino, California. June 8, 1957 Corbett
buys a revolver through mail order. February
24, 1959 Corbett purchases leg irons from a navy
surplus mail order company.
44April 25, 1959 Corbett purchases handcuffs by
mail-order October 8, 1959 Corbett buys
typewriter December 23, 1959 Corbett sells his
1957 Ford. January 8, 1960 Corbett registers
1951 yellow Mercury four-door car under the name
Walter Osborne. February 10, 1960 Early
Morning. Corbett moves out of his apartment in
Denver. Ransom note demanding 500,000 arrives
addressed to Mrs. Adolph Coors, III. Postmark is
February 9, 3PM. Ransom is never collected.
45Capture
Corbett was eventually captured in October, 1960
in Vancouver, Canada, convicted in Colorado
court, and sentenced to life in prison. 1978
Corbett paroled The Bottom Line Together with
other evidence, soil was instrumental in
reconstructing the crime.
46End of Lecture