2Earth’s external processes Weathering – the physical breakdown (disintegration) and chemical alteration (decomposition) or rock at or near Earth’s surfaceErosion – 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 piecesFour types of mechanical weatheringFrost wedging – alternate freezing and thawing of water in fractures and cracks promotes the disintegration of rocks
4Weathering Mechanical Weathering continued Unloading – exfoliation of igneous and metamorphic rocks at the Earth’s surface due to a reduction in confining pressureThermal expansion – alternate expansion and contraction due to heating and coolingBiological activity – disintegration resulting from plants and animals
5Weathering Chemical Weathering Breaks down rock components and internal structures of mineralsMost 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 waterSoluble ions are retained in the underground water supplyOxidationAny chemical reaction in which a compound or radical loses electrons
7Weathering Major processes of chemical weathering Oxidation continued Important in decomposing ferromagnesian mineralsHydrolysisThe reaction of any substance with waterHydrogen ion attacks and replaces other positive ions
9Weathering Alterations caused by chemical weathering Decomposition of unstable mineralsGeneration or retention of materials that are stablePhysical changes such as the rounding of corners or edges
10Weathering Rates of weathering Others factors affecting weathering Advanced mechanical weathering aids chemical weathering by increasing the surface areaOthers factors affecting weatheringRock characteristicsRocks containing calcite (marble and limestone) readily dissolve in weakly acidic solutions
11An obvious example of how weathering differs granitelimestoneAn obvious example of how weathering differswith different mineral solubilities
12Increase in surface area by mechanical weathering
13Weathering Others factors affecting weathering Rock characteristics continuedSilicate minerals weather in the same order as their order of crystallization
14Others factors affecting weathering, cont’d ClimateTemperature and moisture are the most crucial factorsChemical 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 factorsResults in many unusual and spectacular rock formations and landforms
16Differential weathering controlled by jointing patterns
18SoilSoil is a combination of mineral and organic mater, water, and airThat portion of the regolith (rock and mineral fragments produced by weathering) that supports the growth of plants
19Typical components in a soil that yields good plant growth
20Soil Factors controlling soil formation Parent material Residual soil – parent material is the underlying bedrockTransported soil – forms in place on parent material that has been carried from elsewhere and deposited
21Soil Factors controlling soil formation Time Climate Important in all geologic processesAmount of time for soil formation varies for different soils depending on geologic and climatic conditionsClimateMost influential control of soil formationKey factors are temperature and precipitation
22Soil Factors controlling soil formation Plants and animals Slope Organisms influence the soil’s physical and chemical propertiesAlso furnish organic matter to the soilSlopeSteep slopes often have poorly developed soilsOptimum terrain is a flat-to-undulating upland surface
23Variations in soil development due to topography
24SoilThe soil profileSoil forming processes operate from the surface downwardVertical differences are called horizons – zones or layers of soil
25Soil The soil profile O horizon – organic matter A horizon – organic and mineral matterHigh biological activityTogether the O and A horizons make up the topsoilE horizon – little organic matterZone of eluviation and leaching
26SoilThe soil profileB horizon – zone of accumulationC horizon – partially altered parent materialThe O, A, E, and B horizons together are called the solum, or “true soil”
29Soil Soil types Three very generic soil types The characteristics of each soil type primarily depend on the prevailing climatic conditionsThree very generic soil typesPedalfer, Pedocal, Laterite
30Soil Three very generic soil types Pedalfer Pedocal Laterite Best developed under forest vegetationAccumulation of iron oxides and Al-rich clays in the B horizonPedocalAssociated with dry grasslands and brush vegetationHigh accumulations of calcium carbonateLateriteHot and wet tropical climatesIntense 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 colourSoils are the most common materials used in forensic geology because of their dominance on the Earth’s 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
34Coors CaseAdolph 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).DenverMorrison
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.
36A car belonging to a suspect (Joseph Corbett, Jr A car belonging to a suspect (Joseph Corbett, Jr.) was discovered February 17, burning in a garbage dump in Atlantic City, New JerseyWas there a connection ?
37Soil samples obtained from the fender of the car showed four distinct layers
38Deposited first Layer 1 Layer 2 Layer 3 Layer 4 (dump site soil) Outermost layer (deposited last) matched soil sampled at the entrance of the dumpThe 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, ColoradoLayer 1Layer 2Layer 3Layer 4 (dump site soil)Fender SurfaceColoradoSoil ?Deposited last
39With hopes of locating the victim, investigators collected over 350 samples from Rocky Mountain Front, comparing these samples with soil on suspect’s car.Before analyses were completed, Coors’ body was found about 43 km south of Denver.Sept , 1960: Most of Coors’ body recoveredSept. 15, 1960: Coors’ skull located
40Layer 1Layer 2Further soil comparisons indicated similarities between layer 3 on fender and soil where body was found (south of Denver) – material included distinctive pink feldspar from Pike’s Peak granite)Layer 3 (body site)Layer 4 (dump site soil)Fender SurfaceColoradoSoil ?
41Deposited firstFurther 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 1Layer 3 (body site)Layer 2 ( Coors ranch)Layer 4 (dump site soil)Colorado soil ?Fender Surface
42Deposited firstThe 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 1Layer 3 (body site)Layer 2 ( Coors ranch)Layer 4 (dump site soil)Fender SurfaceDenver-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 typewriterDecember 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.
45CaptureCorbett was eventually captured in October, 1960 in Vancouver, Canada, convicted in Colorado court, and sentenced to life in prison.1978: Corbett paroledThe Bottom Line: Together with other evidence, soil was instrumental in reconstructing the crime.