Transcription
Okay, for this lecture, we are going to focus on soil analysis, and we'll tie that into forensic science. So, first, we need to define what is soil. Soil is a mixture. It could be different ratios, percentages of organic and inorganic material. Of something Justin, my son, pointed out is to help you remember that the O in soil is for or, uh, organic, and the I in soil is inorganic. So, I thought that was helpful.
Um, so what are the organic parts of soil? It's anything that was once living. So, it's going to have carbon in it. So, this would be decaying plants and animals. And so they refer to that as humus. Not hummus, hummus is what you eat. So, humus. And if you look at this image, you can see there's different types of organisms. Uh, so you've got the plants, you have insect activity, microbes would be like bacteria, fungi would be an example, would be mushrooms. So, this chart over here is a guide as far as nutrients, how much water it holds, the color of it, uh, microorganisms. This is all that makes up and humus. And that would be the top portion of the soil is where you would find that.
Other ways they can analyze soil is by color. So, what they'll sometimes do is take a portion of the soil. Um, they have the special book. You see these little windows. They'll put it behind it and find the color match. And these are just some very various colors of soil depending on the environment where you would find it, if any amendments like, um, compost has been added to it. And they really have nearly 1100 different colors of soil that they use for classification.
Other things they can look at are the organic components. Is there a lot of plant life? A lot of organisms, etcetera? So, they can break that down and categorize by that. They can also analyze soil by what's called bulk analysis. And this soil needs to be dry. And what they'll do is they'll measure the mass of the soil per unit volume. So, and again, that needs to be dry.
They can also look at the density gradient. So, they'll fill, fill a tube such as a graduated cylinder. I got a picture of it right here. And they'll put different densities of liquids in this tube. And then they'll add the soil. And the minerals have different densities. So, wherever it floats, they know that that particular level of liquid, that would be the density of the soil and the mineral content. So, that's another method.
They can also do something called chromatography. Um, you can actually use chromatography for various things. This is just one application. They can use, uh, chromatography for drug analysis. They can use it for pens, like writing pens, to distinguish the ink. And this is just one way of looking at the soil. I've got two examples here. Um, if anything's from a road, like a gravel or a dirt road, very dull colors, not much humus. You can tell by the lack of color, not much minerals, and it's heavily compacted. Anything that would be like a garden, you tell the warm colors of the golds and browns. There are a lot of various minerals, and it's very fertile.
Um, another way, an additional way of analyzing soil is how much oxygen is available. And that's kind of called aeration. And that's the air around or between the soil particles. And that's what would be available for the roots. So, very fluffy soil would have a lot of oxygen availability. Something that they are starting to, uh, research is the DNA of bacteria, which is the organic component found in soil. So, they are starting to map that.
Um, two last things. And the reason I have this in bold, the very last, this is what we're going to actually do in class. We're going to separate by what's called, um, to sieve, sieving, the particle size. So, I've just got three basic particles. They will actually break that down even more. And it's by millimeter. So, large gravel, uh, can be various sizes. Sand, of course, there's coarse and fine sand. And this other one is silt, very powdery, soft, feels like baby powder. And then the other thing we're going to look at is inorganic components. These are our minerals. So, that would be nitrogen and phosphorus. There's a lot of other different minerals. Uh, potassium is also tested, but we're just going to focus on sorting out by particle size, which is your texture. And we're also going to look at these two particular elements.
Okay, so how is soil factored into forensic science? Well, anytime a criminal is at a crime scene and there's soil available, they track it in from the outside. Then there is a link that is transferred. So, first, they will start with just a visual comparison, the color of it. They would look at the mineral content. They might look at the density. And depending on the area, they could also test for pesticides and herbicides if it's in a rural area or near farming land.
So, how is the soil transported? Um, usually it's found on clothing, shoes, any kind of tools, maybe a weapon. They might also look at the, uh, wheel wells of a vehicle, up underneath the vehicle. Even if they washed it, they might miss any particles. Soil, um, these are just some different types of crimes, and this will be our last slide, and where they would find it. So, if it's a hit and run, they may look under the fender or, like I said, the wheel well, and that might have been transferred to the victim when they were hit. Um, also, they may find grease on the victim, which would come from the car, and they can match that up. If it's a rape case, um, the suspected rapist, if he was kneeling on the ground, if it was outside, would have not only soil but grass stains on the clothes that may have transferred.
A particular murder can use to determine the location of a homicide, especially if it was moved to a different location. So, that would be a secondary crime scene. And if they actually have taken large rocks, which is categorized with soil, and actually use that as a weapon, they can identify the rock on where it was picked up. So, these are just some real basic. Um, if you read your PDF, you would have a lot more information, but, um, hopefully, if you have any questions about this, just ask me in class. And that should do it. Thank you.