Exposing soil’s secrets

Soil tells a story, one that’s often locally or regionally specific. This story can literally stick with us, spreading everywhere we go. One might say they’ve never been to a certain cornfield near Lincoln, Nebraska or walked along a particular bank of the Limpopo River in southern Mozambique. The soil trapped in shoe or vehicle treads, stuck to clothes or bags, lodged under fingernails, or caught in hair, may tell a different story.

Colour, texture, particle type and size, mineral and organic compound composition and the microscopic organisms present can all help pinpoint a soil sample’s source to a likely area. An expert comparing reference and questioned soil samples works to be exclusionary, ascertaining if a questioned sample can – or cannot – be excluded from sharing a source with reference soil. Whittling soil source possibilities down to a particular shore, slope or scene can sharpen investigative focus.

One of the earliest criminal cases involving geological evidence was the 1904 murder of Eva Disch in Germany, which saw forensic scientist Georg Popp aid in connecting a crime scene to a suspect.