How is soil identified and compared in CSI?

How is soil identified and compared in CSI?

That's a very good question because one of things that's important in ascertaining the value of the soil examination is its diversity at the crime scene. For example, if a crime scene takes place on location x and all the soil within a mile of location x is indistinguishable, is the same, the value of that soil as forensic evidence is slight. So what you want to do is to show that there's a tremendous or significant variation of soil at the crime scene. So if we have soil at location x and we have a shoe worn by the suspect with soil on it and they both compare with respect to their colour, mineral content, rock content, then we go a hundred feet out in all directions - north, south, east, west - and we collect soil and we find that those soils are different. Then we go maybe another 300 feet out and we do the same and we find that those soils are different, what we've really done is narrowed down that comparison down to a very small area of the crime scene. It eliminated the possibility that those soils could have come from outlying areas.