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