Secrets Hidden In Soil

Soil scientists, or pedologists, are primarily interested in the way the five soil forming factors (parent material, climate, topotgraphy, organisms, and time) affect the properties of the soil in its natural, undisturbed state. However, Forensic Geologists study soil that has been disturbed or moved during human activity, to solve crimes. Forensic Geologists obtain soil samples from crime scenes and other sites in question where soil may have been transported, by vehicle or by foot perhaps, and are suspect. Soil characteristics are diverse and this diversity enables Forensic Geologists to use soils as evidence in criminal investigations.

THE FIVE SOIL FORMING FACTORS

1. parent material: The material from which the soil is formed. Soil parent material could be bedrock, organic material, an old soil surface, or a deposit from water, wind, glaciers, volcanoes, or material moving down a slope.

2. climate: Heat, rain, ice, snow, wind, sunshine and other environmental forces break down the parent material and affect how fast or slow soil processes go.

3. organisms: All plants and animals living in or on the soil (including micro-organisms and humans!). The amount of water and nutrients ,plants need affects the way soil forms. Animals living in the soil affect decomposition of waste materials and how soil materials will be moved around in the soil profile. The dead remains of plants and animals become organic matter which enriches the soil. The way humans use soils affect soil formation.

4. topography: The location of a soil on a landscape can affect how the climatic processes impact it. Soils at the bottom of a hill will get more water than soils on the slopes, and soils on the slopes that directly face the sun will be drier than soils on slopes that do not.

5. time: All of the above factors assert themselves over time, often hundreds or thousands of years.

The way the five soil-forming factors interact is always different from one place to another, so soils differ greatly from each other. Each section of soil on a landscape has its own unique characteristics. The face of a soil, or the way it looks if you cut a section of it out of the ground, is called a soil profile, like the profile of a person's face. Every soil profile is made up of layers called soil horizons. Soil horizons can be as thin as a few millimeters or thicker than a meter.

Soil profiles and their horizons change as you move across a landscape, and also change as you move downward deeper into the soil at one location. In fact, soil samples taken at the surface may have entirely different characteristics and appearances from soil dug deeper in the soil profile. One common reason soil horizons are different as you dig deeper is because of mixing of organic material in the upper horizons and weathering and leaching in the lower horizons. Erosion, deposition, and other forms of disturbance might also affect the way a soil profile looks at a particular location.

Now, you may be wondering how many soil types are in existence. The United States Department of Agriculture (USDA) maps and collects soil data at many different scales. According to the USDA, there are over 50,000 different varieties of soil in the United States alone! Since parent material, climate, organisms, and the amount of time it takes for these to all interact varies worldwide, soil combinations also vary worldwide. Forensic Geologists have their work cut out for them. So, how do Forensic Geologists use soil to solve crimes? Read on!

TECHNIQUES USED BY FORENSIC GEOLOGISTS

Often, the forensic geologist must determine the distribution of particle sizes in samples for use during comparison studies, mineral studies, and color studies. To perform these studies, the forensic geologist uses methods that GLOBE students and teachers use to study soil soils. Soil samples are taken from intact soil profiles whenever possible and then characterized for structure and texture. The Forensic Geologist uses sieves, graduated cylinders, and hydrometers to perform soil particle size distribution analyses and also performs bulk density tests to determine soil porosity. If the samples collected are discovered to have cementing agents such as calcium carbonate (CaCO₃), iron (Fe), or organics which hold the soil particles together, then these cementing agents are removed using special chemicals.

INSTRUMENTS USED TO STUDY EARTH MATERIALS

Scanning electron microscopes (SEM) and electron microscopes also can be used to examine particles over 100,000 times their original size making them very useful. Forensic Geologists and lab scientists are able to see, in greater detail, the characteristics and variations of soil samples. Fossils and pollen spores that collect in rocks and soil can also be seen, and are sometimes useful indicators when studying soil samples. In fact, scientists were not able to see the distinct differences in very small fossils nor scratches on mineral grains until the SEM was invented. The electron microscope and scanning electron microscope are very useful to the Forensic Geologist who must analyze soil samples with great precision and make important decisions that affect peoples lives.

CRIMINAL CASES SOLVED USING EARTH MATERIALS

Following are some real-life stories of crimes that were solved using Earth materials, thorough investigative work, and dedicated, professional scientists who studied soils and geology to become knowledgeable in their field. So you see, there really is more to soil than what's under foot!

A crime had been committed in the foothills of the Rocky Mountains, near Denver, Colorado. One month later a burning vehicle was found at a dump in New Jersey (on the East Coast of the United States). Soil samples were taken from the fender of the burning car and were studied by Forensic Geologists. Analyses of the soil samples showed there were four layers of soil that had built up under the burning car's fender. The outer, most recently deposited layer of soil was from the New Jersey dumpsite. The three inner layers of soil contained minerals from the Rocky Mountain Front area near Denver, Colorado (If you don't know geography, now is a good time to pull out the United States map and take a look).

Forensic geologists obtained 360 soil samples from the Rocky Mountain Front area to compare them with those found under the fender of the burning car in New Jersey. Soil samples were also taken from the victims ranch. One of the three inner layers of soil under the suspect's car's fender matched the soil sample Forensic Geologists obtained at the crime scene. The second inner layer of soil under the suspect's car fender matched the soil sample Forensic Geologists obtained at the victim's ranch. The first inner layer of soil did not match any of the 360 soil samples taken by the Forensic Geologists but was determined to have originated from the Denver area. The suspect was convicted and jailed based upon the results using soil sample comparisons.

In the case of stolen potatoes on the east coast of the United States, a suspect who possessed the questionable potatoes was convicted of stealing them once analysis of the soil on the potatoes determined that the superphosphate in the soil that was clinging to the potatoes matched the soil from the farm where the potatoes were grown. The farm's soil contained a significant build up of phosphate because the farm was heavily fertilized with nitrogen, potash, and phosphate (phosphate doesn't leach out of the soil as readily as potash and nitrogen).

In another case, tobacco was reported stolen from a farm. Soil samples were taken from the farm where the tobacco had been stolen, and samples were also taken from the leaves of the stolen tobacco and from the suspect's farm. Soil comparison studies indicated that the soil on the stolen tobacco leaves did not match the soil samples taken from the suspect's farm, but matched soil samples taken from the farm where the tobacco was reported stolen. The suspect was arrested based upon the resulting soil sample comparisons.

Microscopic fossils called diatoms were once very prominent on Earth, and collectively deposited to form a sedimentary rock called diatomaceous earth. Some manufaturers use diatomaceous earth for insulating safes, that are used to store valuables. Burglary crimes have been solved by examining white specks from suspects' hair and clothing to determine that the specks were actually diatoms that came from broken safes at crime scenes, and not dandruff as the suspects had claimed.

Information contained in"Secrets Hidden in Soil" was derived from "Forensic Geology" by R. Murray and J. Tedrow, Rutgers University Press, 1975. ISBN 0-8135-0794-4. Also, special thanks to Dr. Richard Arnold, USDA, Natural Resource Conservation Service/Soil Survey Division, Washington, D.C.