Geology
Geology, the study of planetary processes and histories, has applications in forensic science that date back to the 19th century fictional detective Sherlock Holmes. The principles and techniques of geology are most commonly used to identify the sources, or provenance, of rock or soil particles associated with a crime. Other applications include the use of principles borrowed from stratigraphy (the study of sequences of rocks) and structural geology (the study of deformed rocks) to infer a series of events that may be important in civil and criminal cases. Experts in the geology of specific regions can also help to identify locations using their knowledge of rock types and landforms.
Sherlock Holmes, the fictional detective created by the British author Arthur Conan Doyle (1859–1930), was able to distinguish different types of soils and use this information to infer the places to which suspects had traveled. The first known non-fictional use of geological techniques in a criminal investigation, however, did not occur until 1904. In that year, German chemist Georg Popp helped to identify a murder suspect by matching coal dust and particles of the mineral hornblende found on a handkerchief to the same substances at a coal processing plant and quarry that employed the suspect. Several years later, Popp matched layers of goose droppings, distinctive red sandstone fragments, and a mixture of coal, brick, and cement dust to materials at a murder victim's home, the place where the body was found, and the place where the murder weapon was found. Just as importantly, Popp determined that the suspect's shoes contained no distinctive quartz particles from field where the suspect claimed to be walking at the time of the murder. Popp's work, like the work of modern day forensic geologists, made use of the geologic concept of provenance, which is a description of the origin and history of a soil or rock particle, to place suspects in specific locations and disprove an alibi. His use of the sequence of layered goose droppings, sandstone fragments, and dust to infer the sequence in which the suspect visited those locations was an application of the principles of stratigraphy.
Geologists can often determine the geographic source and history, or provenance, of sand grains or soil particles found at a crime scene, especially if distinctive minerals or microfossils are found. This usually involves microscopic examination of soil or rock samples using magnifying glasses, reflected light microscopes, polarized transmitted light microscopes, and, in some cases, sophisticated instruments such as electron microscopes or microprobes. Even if details are not visible to the naked eye, microscopic examination can show that two seemingly similar samples of sand are composed of particles with different chemical composition, size, or shape. In some cases, the geologic details may be specific enough to place a suspect at a certain outcrop or in a specific watershed. This kind of information can be presented as evidence by geologists acting as expert witnesses in civil and criminal cases.
One of the most widely known uses of sand provenance studies in a forensic investigation involves balloons carrying explosive and incendiary bombs over the United States during World War II. Meteorological information was used to determine that the balloons were being launched in Japan and carried across the Pacific Ocean by the jet stream. The balloons carried sand-filled bags as ballast, some of which were automatically released to maintain altitude as temperature dropped each night, and the U.S. Geological Survey was asked to identify the source of the ballast sand found at balloon crash sites. The sand contained an unusual mixture of mineral grains, diatoms, and foraminifera (single celled organisms that secrete siliceous and calcareous shells), and mollusk shell pieces but no coral fragments. Government geologists studied maps and reports published before the war, and determined that sand with that unique composition existed at only two places along the Japanese coast. Those locations turned out to be very close to the actual launching points. Identification of sand grains and soil particles has been an important part of high-profile criminal cases such as the 1978 kidnapping and murder of Italian prime minister Aldo Moro and the unsuccessful attempt by Mexican federal police to cover up the 1985 kidnapping, torture, and murder of U.S. Drug Enforcement Agency operative Enrique Camarena Salazar and his pilot Alfredo Zavala Avelar.
Geologic details in images can also help investigators determine the locations in which photographs or video recordings were made. In the days after the September 11, 2001, terrorist attacks on New York City and Washington, D.C., for example, American geologists who had worked in Afghanistan were able to identify rock outcrops shown in video tapes of the terrorist leader Osama bin Laden, placing him in a certain part of that country. This use of geologic information was widely publicized and subsequent tapes were made against a cloth background in order to make identification more difficult.
Join eNotes
Over 3,500 study guides, question and answer forums, literature criticism, reference content, and much more!
