What is forensic geology?
- Forensic geology is the study of evidence relating to minerals, oil, petroleum, and other materials found in or incorporated into the earth (such as soil, glass, water, or fossils) that can be used to answer questions raised by the criminal or civic legal systems.
- In general, the field of forensic geoscience involves criminal and civil investigations utilizing the disciplines of geology, geomorphology, botany, biology, and statistics.
- Forensic investigations can take place at the macro scale of satellite imagery and GIS through to the micro scale analysis of trace materials including soils/sediments and DNA analysis.
- Forensic geology examiners usually do two types of studies while investigating a case: 1) The study of comparing two samples, one of them being the questioned sample associated with the crime (usually material that has been transferred) and the other being a control (where you think the sample originated from). Are the samples similar? How do they compare? Could they have a common source? 2) The study of samples (usually from collections of soils from various locations) that are typically associate with the suspect or the suspect’s alibi. Where did the questioned rock or soil (or other collected material) come from?
What do forensic geologists do?
- Forensic geologists combine technology, creative strategies, science, and personal experience to help their clients solve problems involving groundwater, surface water, soil, and other environmentally related subjects.
- When doing a criminal/legal case, they are more specifically concerned with soils that have been disturbed or moved (usually by human activity). Then, they compare their evidence to natural soils, or matching them with soil databases, to help locate the scene of crimes.
- They use instruments and methods common to the profession of geology, such as binocular microscopes, petrographic microscopes, X-ray diffraction, scanning electron microscopes, and microchemical analysis.
- Sometimes forensic geologists cannot come to any concluions. This could be because 1) no transfer took place, 2) there was a transfer but evidence was later removed, 3) two or more types of evidence were transferred (like from 2 separate areas), resulting in a composite sample, 4) the environment of the area under investigation changes rapidly and the sampling was inadequate.
How did forensic geology get started?
- The application of geology and soil science to criminal and legal investigations started in the late nineteenth century with increasing developments in crime-lab technology.
- The idea of forensic geology started to become popular with the writings of Sir Arthur Conan Doyle. Namely, with the publication of the Sherlock Holmes series between 1887 and 1893. The techniques used by Holmes were never used before the books were written, most of the techniques used in the series were invented by Doyle, who was also a physician.
- In 1904, Georg Popp was the first person to use earthen materials as evidence in a criminal case. Popp, a chemist by training, was asked to examine the evidence in a murder case where a seamstress named Eva Disch had been strangled in a bean field with her own scarf. He used collected bits of coal, particles of snuff, and grains of minerals, particularly the mineral horneblende, as his evidence to determine a suspect. Once he found the suspect, he studied the soils on the suspect’s pants, which allowed him to determine where the body of Eva Disch was located.
What are other similar fields?
- Similar fields consist of Forensic Pedology, Forensic Geoscience, Geoforensics, Soil Forensics, and Environmental Forensics.
- Forensic Pedology: the study of soil, both in situ as a natural material possibly disrupted by unusual events, or as a transferred material on suspects, victims and associated items (tires, vehicles).
- Forensic Geoscience: encompasses forensic geology and forensic pedology, as well as unusual applications such as statistics and bedrock geology
- Geoforensics: encompasses forensic pedology, geology, forensic geoscience and includes geomorphology, GIS, remote sensing, human geography (including sociology) and geostatistics.
- Soil Forensics: includes all the methods available to study the use of soil in forensics, meaning not only the study of soil (Pedology) but also the methods outlined in forensic geology, forensic geoscience and geoforensics, as applied specifically to soil, as opposed to bedrock geology.
- Environmental Forensics: the use of any of the above methods, as well as chemistry, biology, physics and the environmental sciences in the assessment of environmental impact.
How can forensic geology relate to soil?
- Forensic scientists must first determine if uncommon and unusual particles, or unusual combinations of particles, occur in the soil samples and must then compare them with similar soil in a known location. To do this properly, the soil must be systematically described and characterised using standard soil testing methods to find out whether a soil sample can be used as evidence. Methods for characterizing soils for a forensic comparison involve subdividing methods into two major stages, descriptive (morphological) and analytical.
- Stage 1: Initial Characterisation of Composite Soil Particles in Whole Samples for Screening
- In the initial screening or comparison examination of whole soil samples, soil morphology, low magnification light microscopy, X-ray diffraction (XRD), Diffuse Reflectance Infrared Fourier Transform (DRIFT) spectroscopy, and magnetic susceptibility (volume and mass) are used to compare samples via bulk morphology, mineralogy and organic matter characterisation.
- Soil Morphology: Soil interpretation provides a visual, quick and non-destructive approach to screen and discriminate among many types of samples. There are six key soil morphological descriptors 1) consistency, 2) color, 3) texture, 4) structure, 5) additional coarse fragments, like fossils or iron bearing minerals, and 6) abundances of organic mater, such as roots. ** The use of petrography is a major and often precise method of studying and screening soils for discrimination in forensics
- Mineral and Organic Matter Identification and Composition: Determine the mineralogical and organic matter components and their compositions. You do this by using XRD, DRIFT, and rpid mass and volume magnetic susceptibility methods.
- Stage 2: Detailed Characterization of Composite and Individual Soil Particles
- X-ray Diffraction (XRD)
- Scanning Electron Microscopes (SEM)
- Transmission Electron Microscopes (TEM)
The “Hit and Run” Case Study
- This case study involves two suspects that left the scene of a fatal car collision. One of the suspects fled the scene and was chased through a housing complex and a river. He was later seen running down the river bank, running along side the gravel/stone river bank, jumping into the river, and then going up the opposite river bank and disappearing into the adjacent parklands.
- Two control samples were taken from the alleged “crime trail” located on the the gravel/stone river bank and in the river channel. Two additional “alibi samples” were collected from the alibi trail/scene and up the river bank to determine if the suspect actually had been along the crime trail.
- The suspect was later apprehended by police but denied being along the alleged crime trail.
- A sufficient amount of the soil was recovered from the soles and sides of the shoes for forensic soil analyses by gently scraping the fine soil from the shoes using a plastic spatula.
- The soil analysis mentioned earlier were applied to the Hit and Run case. The visual comparison of the questioned samples from the shoe and control samples had remarkably similar color and texture. After analyzing the samples with XRD and DRIFT, it was concluded that the mineralogical and chemical compositions of the soil samples were closely related to one another. It can be determined that their similarity is significant because they both contain quartz, mica, albite, orthoclase, dolomite, chlorite, calcite, amphibole and kaolin.
- Overall, these comparisons indicate that the two samples have a high degree of similarity and are most likely to have been derived from the same general location. In contrast, there is a lower degree of similarity with the two alibi soils samples.
- By using this evidence in trial, the suspect was found guilty of the hit and run by the supreme court of South Australia.