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WHEN SOIL IS NOT JUST DIRT Police in California found a dead body on the platform of an oil well. Investigators noticed the rocks used to construct the platform seemed unique. Test showed that the rocks were a special type that came from a site 300 miles for the well’s location. They knew finding matching samples of the rocks on a suspect would be key to solving the case. Police arrested an acquaintance of the victim. The suspect kept repeating, “I wasn’t anywhere near the crime scene!” The police suspected otherwise. Physical evidence linking the suspect to the crime scene was needed. After they obtained a search warrant, the police took possession of work boots that had been worn by the suspect. They took the boots to a laboratory. Once in the lab, forensic scientists attempted to match soil samples from the suspect’s boots to soil from the area where the body was found. The suspect was not worried. To him, dirt was dirt. He was unaware of the testing that could be done to compare the soil from his boots to the soil found on the body. Forensic geologists performed chemical and microscopic tests on the soil on the suspect’s boots, as well as samples taken from his car.
Examining soil evidence
The test proved that the samples from the suspect came from the site where the body was found. Faced with convincing evidence, the suspect admitted his guilt and was sentenced for the crime.
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SCENARIO Organize students into small groups to read the scenario, and answer the following questions: What are the different kinds of soils? What kinds of soil would you expect to find on a beach? In a desert? In a rainforest? How are these types of soils similar and how are they different? What do you think makes each of these soils different?
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Many scientists agree that no two places on Earth have precisely the same soil. Soil recovered from a crime scene, a victim, or a suspect can be analyzed to determine commonality and significance. Soil is part of the top layer of Earth’s crust and contains minerals, decaying organisms, water, and air, all in varying amounts. Soil is classified by its texture or grain size and is divided into sand, silt, and clay. Soils form in horizons, or layers, and each horizon has characteristic properties that differ.
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Soil Examination
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The Big Ideas
CHAPTER
©Gary Conner/PhotoEdit, Inc.
Soil is more than just dirt or rock. It is the medium present on Earth’s surface that supports plant growth. Soil is primarily made up of weathered rock, but it is also composed of air, water, bacteria, and humus. The soil formation process is what makes all soils unique. Forensic scientists use soil’s unique characteristics to help solve crimes. Soil can be analyzed for its general makeup—sand, silt, or clay—and then further analyzed for its mineral and chemical composition.
CHAPTER
Chapter Overview
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KEY SCIENCE CONCEPTS Earth Sciences: soil composition and characteristics; soil formation Chemistry: pH
Objective
s
By the end of thi
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s chapter you wil
l be able to 12.1 Recognize various soil types and describe so methods for exam me ining soil samples . 12.2 Distinguish sand samples by size, color, and 12.3 Perform composition. a soil analysis, inc luding macrosc microscopic exam opic and ination, as well as chemical and physical an alysis. 12.4 Explain ho w soil evidence can link suspec ts to crime scen es.
Vocabula
ry
clay the sm allest ty pe of soil particles that have sand gran to absorb the capaci ules of and hold ty fine rock particle water geology th s e study si of lt a so ty il and rocks pe of so il whose ticles ar pare larger humus ma than clay smaller terial in than sand and the uppe layers of r soil made decaying up of th so il a mi e remains xture of of plants minerals animals ter, gase , waand s, and th e remain of dead leaching th s or ga ni e remova sms that Ea rt l and clay covers h’s surf of minera ace as water ls drips th soil profile the soil rough a cross section horizont of mineral a al layers naturall , or hori in the soil y occurr zons, crystall that have ing, ine soli co mpositio distinct d formed time on ns and pr over Earth op erties weathering rock a ha formatio rd substa n of soil through nce made of minera th e ac tion of up ls water on wind and rock
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Teaching Resources Instructor’s Resource CD-ROM includes: ● PowerPoint Presentation ● Lesson Plan and extended Objective Sheets ● Teacher Notes and Activities ● Activity Forms ● Rubric ExamView CD-ROM E-book on CD-ROM Web site: school.cengage.com/forensicscience 339
Explore Allow students to make their own observations of soil. In separate, clear containers, place samples of sand, silt, and clay. Ask students to study the samples and write down their observations of each soil. Pour water into the containers and ask students to make further observations. Give the students the terms “sand,” “silt,” and “clay,” and ask them to determine which container has each soil type.
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People in some cultures eat dirt. They do it because they say it tastes good or they think it will bring them good luck. But don’t try it. Eating dirt can make you sick. On the other hand, the fact that babies of a certain age seem compelled to eat dirt has been theorized to be an adaptation allowing the immature immune system to encounter pathogens in the soil.
Soil is produced by a complicated process that is influenced by factors such as temperature, rainfall, and the chemicals and minerals present in the material from which it forms. Because of all the factors that affect soil formation, soil from different locations can have different physical and chemical characteristics that are useful to forensic scientists. Soil analysis has been used to identify livestock thieves and even the location of hot air balloon construction sites. The uniqueness of soil composition has helped locate burial sites and link suspects to crime scenes. In one case, cattle rustlers stole a herd of cattle from Missouri and took it to Montana. The rustlers changed the brands on the cattle, thinking they would not get caught. However, they did not think of everything. Forensic scientists analyzed a sample of cow manure taken from the back of a truck thought to be used in the theft. They found small fragments of a rock made from silica in the manure. This type of rock could only have come from Missouri. Police used this soil evidence to convict the rustlers. During World War II, Japanese scientists devised a plan for delivering explosives to the United States. The explosives would be carried in the air from Japan to the United States using hydrogen-filled balloons. The balloons also carried bags of sand as counterweights. More than 9,000 of these balloons were launched. Physical evidence has shown that about 300 balloons actually reached America. The explosives carried by the balloons did little property damage. However, six people lost their lives when one of the explosive-laden balloons detonated. By analyzing the sand used in the counterweights, geologists were able to determine that it came from one particular beach in Japan. With this information, the American forces bombed that beach and destroyed the site where the balloons were constructed.
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HISTORY OF FORENSIC SOIL EXAMINATION
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Sir Arthur Conan Doyle is best known as a writer, introducing Sherlock Holmes for the first time in A Study in Scarlet (1887). Doyle’s inspiration for Sherlock Holmes was Dr. Joseph Bell, a professor of Doyle’s when he attended medical school at the University of Edinburgh. Sherlock Holmes’ stories have been translated into more than 50 languages, and made into plays, films, television series, a musical comedy, a ballet, cartoons, and comic books. By 1920, Doyle was one of the most highly paid writers in the world. For more information about Doyle, go to the Gale Forensic Science eCollection at school.cengage .com/forensicscience.
INTRODUCTION
Real and fictional investigators have been using soil samples to identify criminals since the late 1800s. Between 1887 and 1893, Sir Arthur Conan Doyle wrote about the use of geology in the investigation of crime in his novels. His character, Sherlock Holmes, used soil and mud samples to help link an individual to a specific location where a crime had been committed. An Austrian, Dr. Hans Gross, is believed to be one of the first forensic scientists to apply science to crime Sir Arthur Conan Doyle created the character Detective Sherlock investigation. His book Holmes, but Doyle wasn’t only a writer. Go to the Gale Forensic Criminal Investigation, Science eCollection on school.centage.com/forensicscience and written in 1893, conresearch Doyle’s life and Sherlock Holmes. Give a short presentation tained groundbreakon this famous author and his famous creation. Include answers to ing material in this new the following questions in your presentation: science. He was also a How did Conan Doyle feel about Sherlock Holmes? university professor and After more than 100 years since the first publication, why is Sherlock founded the Institute Holmes still so popular? of Criminology in Graz, 340
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Differentiated Learning Teaching English-Language Learners Some students may be unfamiliar with the terms cattle rustler, cattle brand, and counterweight. Ask volunteers to explain each term and any others that non-native speakers may not know.
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Ask students to describe the soil around their houses. Continue the discussion with the following questions: • What kinds of plants are growing around your house? • What do you think forensic scientists would find unique about the soil around your house? • How do you think they could determine that soil came from your house and not a neighbor’s house?
CHAPTER
Engage
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Austria. Dr. Gross firmly believed in the value of physical evidence, including soils found at crime scenes. A German investigator, Georg Popp, is credited with being the first forensic scientist to use soil evidence to solve a crime. During a murder investigation, he examined a handkerchief left at the crime scene and found it contained bits of coal and particles of hornblende, a greenishblack-colored mineral. Using science, Popp linked this evidence to a suspect who was known to work in a coal-burning factory and also in a gravel pit that contained hornblende. Popp also matched soil samples taken from the suspect’s trousers to samples collected at the crime scene. When confronted with all of the evidence, the suspect admitted his crime.
In the 1880s, a railroad company laying tracks in northwest Colorado gave the town Silt its name because of the nature of the soil in the area. Obj. 12.1, 12.2, and 12.3
SO I L COMP OS IT ION
Tell students that hornblende is a name given to collections of minerals. The chemical makeup of hornblende is quite variable. It often makes up the dark part of igneous rocks, which are composed of light and dark crystals.
Explore The Earth contains many layers—inner core, outer core, mantle, and crust. The top layer of the Earth is the crust. The crust makes up only about 1 percent of Earth’s volume. Organize students into groups. Assign each group a layer of the Earth to research, and report their findings to the class.
Soil is part of the top layer of Earth’s crust, where most plants grow. Soil contains minerals, decaying organisms, water, and air, all in varying amounts. Soil texture describes the size of the mineral particles that make up soil. There are three main soil grain sizes: sand, silt, and clay. Sand describes the largest grain size and clay the smallest grain size. There are also three subcategories of soil—loam, peat, and chalk. Loam is a type of soil that is made up of sand, silt, and clay. Along with mineral particles, soil can also contain organic material, such as decaying plants and animals. Soil with more than 20 percent decaying organic material is called peat soil. Chalk soil is alkaline and contains various-sized pieces of a solid, but soft, rock called chalk. Figure 12-1 summarizes information about these soil types. Figure 12-1. Soil Type Comparison
All photos ©Susan Van Etten
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Explore
Soil Type
Feel
Composed of
Location
Sand
gritty
weathered rock
deserts, beaches, riverbeds
Clay
sticky
small particles various adhering to each other
Silt
crumbly, slippery like flour
medium-sized mineral particles
Peat
compressible
decaying organic material
Loam
loose
Chalk
various colors, white to brown
Other Characteristics large visible particles, loses water quickly
Science Earth Science When the remains of plants partially decompose, they form a brownish-black soil called peat. Peat deposits are still forming today. In some parts of the world, people burn peat to heat their houses and cook their meals.
small particles, clumps, poor drainage
sediment in riverbeds good drainage, easily farmed
bogs, areas where water is retained by organic matter failing to decompose sand, silt, and various clay mixture
acidic, used with other soil types in fertilizer because of its ability to retain water best soil for agriculture
alkaline (basic) soil with mineral stones
poor for agriculture, requires the addition of fertilizer and humus
below the top soil
Science
Soil Examination
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Differentiated Learning
Differentiated Learning
Teaching English-Language Learners Students may not be familiar with the terms sand, silt, and clay. Help them to understand these words by showing them examples of each. Explain that sand particles are the largest of the three types. Silt particles are smaller than sand, and clay particles are the smallest particles of all.
Teaching Gifted Students Ask students to research the soil texture triangle. Ask them to make a poster of the triangle and explain it to the class. Suggest they bring in examples illustrating soil mixtures with different percentages of sand, silt, and clay, and show how to determine the soil name by using the texture triangle.
Earth Science Peat deposits are covered by layers of sediments. Over time, the weight of these sediments forces out water and gases from the peat, forming a denser material called lignite, or brown coal. The pressure from sediments compresses the lignite further, forming soft coal, or bituminous coal. Bituminous coal is the most plentiful type of coal in the world. Further pressure on bituminous coal produces the hardest form of coal, called anthracite. Both bituminous coal and anthracite are made up of 80 to 90 percent carbon, and release large quantities of heat when they burn. 341
SOIL PROFILES
CHAPTER 1
Soils form in horizons, or layers, that are more or less parallel to Earth’s surface. The soil in each horizon has characteristic properties that differ from those in other horizons, as shown in Figure 12-2. Soil in a given area will have a unique profile or sequence of layers. Soil horizons within the profile are labeled with an uppercase letter, named as follows:
Teaching Tip
2
The uppermost horizon is called the O horizon. It is made up mostly of decaying organic matter, sometimes referred to as humus.
Naming the soil horizons can be confusing because different sources use different letters for the various layers. For example, what this text is calling Horizon R, is called Horizon D in another source. Therefore, students should understand that different sources use different letters for the same horizon type. Tell them that for this reason, becoming familiar with the graphic cross section, and horizon composition, is important.
3
Beneath the O is the A horizon. The soil here is dark in color. The A horizon is also called topsoil. Topsoil is a mixture of humus and mineral particles. Seeds sprout and plant roots grow in the A horizon.
Ask students what they think the “0” in 0 Horizon stands for. (It stands for organic.)
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Chemistry According to one definition of acids and bases, an acid releases hydrogen ions when it combines with water, and a base releases hydroxide ions in combination with water. The concentration of hydrogen ions in a solution is commonly expressed in terms of pH.
O A E
The C horizon is next. This layer is made of partially broken-up rock. Plant roots do not grow in this layer. Also, very little humus is found in this layer. If there is a solid rock layer underneath all of the other horizons, it is called the R horizon.
B C
Teaching Tip
Science
The B horizon lies beneath the E horizon. Another name for this layer is the subsoil. The subsoil contains clay and mineral deposits that have leached out from layers above it as water drips through from the horizons above.
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Remind students to write pH with a lowercase p and an uppercase H.
Next is the E horizon. The soil in the E horizon is light in color. It is made up mostly of sand and silt. Water dripping through the soil in this layer carries away most of the minerals and clay originally present. This process is called leaching. Figure 12-2. A typical soil profile with horizons labeled.
R
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CHEMISTRY OF THE SOIL 12 The materials that make up a type of soil determine that soil’s chemical properties. An important chemical property of soil is whether it is acidic or basic (alkaline). Chemists use a special scale, called the pH scale, to indicate how acidic or basic a substance is. The pH scale ranges from 0 to 14 (Figure 12-3). Anything with a pH of less than 7 is acidic. Substances with a pH greater than 7 are basic. A substance with a pH of 7, such as pure water, is considered neutral.
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Figure 12-3. The pH scale. strong acid pH value = 1 2 Examples Acidic substances Battery acid Lemon juice Orange juice Vinegar Breads, pasta Rain (not acid) Milk 342
3
weak acid 4 5
6
neutral 7
pH value (approximate) 1 2.5 3.0 3.5 5.0 5.5 6.5
8
9
weak base 10 11
Examples Basic substances Baking soda, sea water Milk of Magnesia Detergents Ammonia water Bleaches, oven cleaner Lye (drain cleaner)
strong base 12 13 14
pH value (approximate) 8.5 10.5 10.0 11.0 12.0 13.5
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Science Chemistry The pH scale runs from 0 to 14. The lower the pH number, the more acidic, and the higher the number, the more basic. A low pH corresponds to a high hydrogen ion concentration, and a high pH corresponds to low hydrogen ion concentration. If a substance has a high concentration of hydrogen ions, it is called an acid, and a substance with a low concentration of hydrogen ions is called a base. The pH scale is logarithmic, meaning the numbers are based on factors of 10. A solution with a pH of 4 has 10 times the hydrogen ions that a solution has with a pH of 5.
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Teaching Tip
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The pH of a soil can help determine if a plant will grow and survive. Whether certain minerals and nutrients are available to plants is partly determined by the soil’s pH. Plants need nutrients like nitrogen and phosphorus to grow, but before a nutrient can be used by plants, it must be dissolved in the water contained within the soil. Most minerals and nutrients are more easily dissolved in acidic soils than in neutral or slightly alkaline soils. If the pH of the soil is above 5.5, nitrogen in the soil is made available to plants. Phosphorus in the soil is available to plants when soil pH is between 6.0 and 7.0. Figure 12-4 shows how the absence of certain nutrients can affect plants.
Explore Explain the NPK three-number system of identifying fertilizers to students. NPK stands for nitrogen, phosphorus, and potassium. All fertilizers have three numbers listed on the bag. For example, if a bag is marked 18-24-6, this means that the fertilizer contains 18 percent nitrogen, 24 percent phosphorous, and 6 percent potassium. The remaining ingredients in the fertilizer are known as ballast, or filler, and may or may not be helpful to plants. It is important to know soil pH, so the right kind of fertilizer can be applied. Nitrogen helps plants produce more chlorophyll, which allows the plant to grow quickly. Phosphorous helps with root development and increases flowering ability and bloom size. Potassium guards the plant against diseases and aids in drought protection and cold tolerance.
Figure 12-4. Effects of nutrient deficiencies in plants. Nutrient Deficiency
Appearance of Plants
Nitrogen
Leaves of plants are yellow
Phosphorus Potassium
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Calcium
Small, frail plants with reddish leaves Leaves at bottom of plant dying from lack of chlorophyll (no longer green) Stems and leaves droop, unable to support upright position
Materials that make up a soil are not the only factors that affect its pH. Rainfall can change the pH of a soil. Water passing through the soil can carry away some basic substances, leaving the soil more acidic. Pollution, acid rain, and fertilizer use can also change the pH of soil.
SAND Sand is formed by the action of wind and water on rocks, called weathering. As wind and water move rocks around, the rocks collide with other rocks. These collisions break the rock into smaller and smaller pieces until small grains, called sand, remain. As rock weathers, it breaks along boundaries between different types of mineral crystals. If the sand grain contains only one mineral, it is considered a crystal. If the grain contains two or more minerals, it is called a fragment. The size of sand grains can be anywhere from 0.05 mm to 2 mm in diameter. Grains of sand can be rounded or angular, depending on the amount of weathering and the mineral composition of the rocks that formed the sand. Figure 12-5 on the next page shows different types of sands.
Explore
ROUNDING As pieces of rock are moved by wind or water, they strike against one another. If the pieces hit in the center, they bounce off. If they strike along an edge, the edges may break off. As the edges break off, the rock pieces become more rounded. The entire rounding process may take millions of years to complete. Sand grains carried by water lose their jagged edges and become rounded more slowly because the water acts as a buffer, so sand grains collide more gently. Wind-blown sand becomes rounded more quickly because the grains strike each other directly without a water buffer. Soil Examination
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Differentiated Learning
Differentiated Learning
Teaching Gifted Students Ask students to choose a plant they would like to research. Have them make sure to include the effects that nitrogen, phosphorous, and potassium have on the plant, and what soil pH is best for the plant.
Teaching At-Risk Students Allowing students to examine different types of sand and soils, and feel them their hands, will help students connect to the material and help them stay on task.
Sands are generally measured by sieving. A sand sample of known mass is passed through a set of sieves of known mesh sizes. The sieves are arranged in decreasing mesh diameters. The sieves are mechanically vibrated for a fixed period of time. The mass of sediment retained on each sieve is measured and converted into a percentage of the total sediment sample. This method is quick and accurate enough for most purposes. Essentially, it measures the maximum diameter of a sediment grain.
Science Earth Science Rocks on Earth’s surface undergo changes in their appearance and composition. The change to rocks exposed on Earth’s surface is called weathering.
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a. Bermuda sand
b. Myrtle Beach, SC, sand
c. Vero Beach, FL, sand
d. Hawaii sand
e. Bahamas sand
f. Rhode Island sand
Sand grains are classified as young, or immature, and old, or mature. Immature sand contains a large portion of clay, and the grains have a high percentage of fragments. This type of sand is found close to where it was formed, usually in areas where it is not exposed to waves or currents, such as the bottom of bays and lagoons, or in swamps or river floodplains. Mature sand does not contain clay and has fewer fragmented edges. Mature sand is found in areas, such as beaches and desert dunes, where much water and wind weathering has taken place.
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MINERAL COMPOSITION OF SAND 10
Teaching Tip Ask students if they have ever seen sand dunes. Explain that sand dunes form when sand is carried by the wind from the beach toward the land. When the wind encounters an obstacle, like a clump of vegetation or large rocks, the wind slows down and deposits the sand grains it is carrying. Sand grains deposited over a long period of time eventually produce large hills of sand sometimes 6 meters (20 feet) high.
Sand from different locations contains different combinations of minerals. The most common mineral found in sand is quartz. Many other minerals, such as feldspars, micas, and iron compounds, may be present in smaller quantities. Sand can also be made of organic material, such as coral and seashells. There are four basic sources of sand. These four types are summarized in Figures 12-6 and 12-7.
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Figure 12-6. Sand composition. Source Continental sand Volcanic sand
15 Skeletal (biogenic) sand
16
Precipitate sand
Identifying Features quartz dark color with green olivine, no quartz shells indicate evidence of warm-water life oolithic, egg-shaped, or round spheres of calcium carbonate from rock
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Continental Sand Continental sand is composed mostly of quartz, micas, feldspars, and darkcolored minerals like hornblende or magnetite (Figure 12-8). If feldspar is present, the sand probably came from a temperate or polar climate or from a high altitude. In warm, tropical climates, feldspar weathers away quickly. A high percentage of quartz means the sand is very old, because quartz weathers very slowly and often remains after other minerals have weathered away.
Teaching Tip Tell students that feldspar is pink because it contains high levels of potassium. Feldspar and quartz are also two of the main components of granite. These sands are commonly the result of eroded granite.
Composition granite, quartz, feldspar, mica, dark minerals dark color, black basalt, green olivine, volcanic ash broken shells, coral, coralline algae, sea urchin remains calcium carbonate
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Differentiated Learning Teaching Gifted Students Have interested students use a flex cam and a microscope to examine various sand samples. Ask students to describe and compare them.
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1 All photos ©Cengage Learning
There are two types of black sand beaches, one where the grains are very sharp and one where the edges have been rounded over. The way lava enters the ocean determines which type of sand is formed. When very hot lava flows directly into the cold ocean, the lava is shattered into pieces, creating black sand beaches with sharp volcanic glass. Black sand beaches can also form from erosion of volcanic rock. As water (either ocean waves or a stream cutting through a lava bed) moves over the rock, it breaks up into smaller pieces. This creates pieces of black sand with edges that have been rounded by erosion.
CHAPTER
Explore
Figure 12-5. Examples of different sands.
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Figure 12-7. Mineral components of sand.
Explore
d. Granite is usually found in massive deposits.
b. Magnetite is opaque black or gray. It is a form of iron oxide.
e. Mica appears in flakes and flat sheets.
c. Quartz can be white, gray, rose, or clear. It is a very abundant mineral.
f. Coral is the rocklike skeletal remains of sea life.
Volcanic Sand Volcanic sand is usually dark in color as a result of the presence of black basalt or green olivine (Figure 12-9). The source of this sand is from midocean volcanoes, hot spot volcanoes, like those found in Hawaii. It sometimes contains volcanic cinders or other volcanic debris. Volcanic sand is very young and contains little or no quartz, except for obsidian (black) particles.
Figure 12-8. Continental sand from Big Sur, California.
Skeletal (Biogenic) Sand Figure 12-9. Volcanic sand from Hawaii.
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This type of sand is made of the remains of marine organisms, such as microorganisms, shells, and coral (Figure 12-10, below). It is younger than other types of sand. Skeletal sand originates in water and occurs all over the world. Skeletal sand made up of coral, however, occurs only in tropical regions. Because of the high amounts of calcium carbonate, skeletal sand gives off bubbles when mixed with a few drops of an acid.
Precipitate Sand Water contains dissolved minerals, and when the water evaporates, these minerals precipitate, or come out of the water solution, and form crystals. Calcium carbonate will sometimes precipitate out of seawater, forming a coat of hard particles that resemble the layers of an onion. These layers eventually form small, round structures called oolites. Oolite formation is not an example of weathering, but rather of deposition. Sand containing these oolites is called oolithic sand and can be found in various places, including near the Great Salt Lake in Utah (Figure 12-11). Figure 12-10. Skeletal sand from Bermuda and the Bahamas.
Soil Examination
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Explain to students that another type of skeletal sand is diatomaceous earth. This fine sand is made up of tiny silica shells of diatoms, primitive microscopic algae, and is common in both fresh and saltwater. Diatomaceous earth has many uses, such as a scrubbing agent in toothpaste, in swimming pool filters, and as an insect control for plants.
Evaluate Ask students what gas is given off in the bubbles when acid is placed on skeletal sand—carbon dioxide, CO2. If they do not know, write the chemical formula for calcium carbonate (CaCO3) on the board. Ask if they can deduce the gas formed from this formula.
Teaching Tip
Figure 12-11. Precipitate sand from the Great Salt Lake, Utah.
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Teaching Tip
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a. Feldspar is light in color and opaque. It comprises about 60 percent of Earth’s surface.
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All photos ©Cengage Learning
There are also green sand beaches. Ask interested students to find out how green sand is formed, and where these beaches exist.
Point out that in the word oolith, the prefix oo- refers to egg and the suffix -lith refers to rock or stone. When put together, the term means an “egg stone” because of its resemblance to a tiny chicken egg.
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Differentiated Learning Teaching At-Risk Students Organize students into a group. To have them learn about the different types of sand, encourage them to draw a picture of each. Have volunteers explain the drawings. Display them in the classroom.
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SOIL COLLECTION The following are some of the steps a crime-scene investigator uses to collect soil evidence at a crime scene. See Chapter 2 for information on correctly labeling and packaging samples. At a crime scene, investigators must follow certain procedures for collecting, labeling, and packaging soil evidence. They must:
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1. Collect all samples as soon as possible before the environment of the crime scene can be changed by humans or animals walking through the scene or by weather conditions, like rain. 2. Collect at the surface baseline samples and samples that appear different or out of place from the rest of the environment of the crime scene. 3. Collect at least four tablespoons of material from several locations at the scene. 4. Sketch the crime scene and note on the map where the soil samples were obtained. 5. Be careful not to remove soil stuck to shoes, clothing, or tools found at the crime scene and package these items separately in appropriate containers. 6. Carefully remove soil from vehicles and package these soil samples separately. 7. Document all samples by taking photographs, drawing sketches, and labeling the evidence collection containers. 8. Collect additional soil samples from the four compass points (north, south, east, and west) within a few feet of the crime scene. Collect another set of samples 20 to 25 feet from the crime scene.
3
Explore Explain that soil collection methods differ depending on the location and type of soil evidence. If the soil made by the footwear creates a pattern print of the bottom of the shoe, it should be photographed and lifted as a print (impression). Lumps of soil stained with blood, semen, or other biological evidence should be collected intact and transported to the lab as dry samples. The only time soil evidence should not be allowed to air dry is when insect (maggots) evidence is present. Samples containing maggots should be placed in aluminum foil with a small piece of beef liver and then placed in a plastic container. There must be air available in the container. These samples should be photographed and sent to the lab immediately.
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Instruct students to write out an actual or fictitious crimescene scenario that involves soil evidence. Then, have students exchange scenarios with a classmate and describe what soil evidence is present and how investigators should properly collect each soil sample. For additional information on soil collection and analysis, go to the Gale Forensic Science eCollection at school.cengage .com/forensicscience.
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SOIL EXAMINATION
Soil recovered from a crime scene, victim, or suspect can be analyzed to determine if the suspect was at a particular location. Forensic scientists carefully compare the characteristics of the soil samples taken from the suspect or crime scene to those taken from a known location. The presence of soil unique to a certain area can show that a suspect or victim must have been in that area. The absence of a particular kind of soil can be used to prove or disprove an alibi. Layers of soil or mud taken from shoes or the wheels of vehicles can show that a Why is it important for crime-scene investigators to properly collect suspect was present at a and handle evidence? Go to the Gale Forensic Science eCollection series of locations. on school.cengage.com/forensicscience and enter the search term Scientists compare “soil analysis.” Click on Magazines and read about the investigation the size, shape, and into the burial of five murder victims. Use information from the article color of soil by looking at and what you have learned about soil evidence collection procedures samples macroscopically to write a brief essay describing the methods the investigators used for soil type, amount of to make sure their evidence was collected properly and not contamiplant and animal matenated. Be sure to cite your resources. rial, and particle size. 346
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Have students explain why if soil on a vehicle is in a clump, care should be taken to keep the clump intact. The layers in the soil clump can help establish a timeline.
CHAPTER
Evaluate
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Soil can also be identified and compared by studies using density columns, moisture content, and chemical testing for mineral content. Additional testing involves using specific laboratory techniques, such as X-ray diffraction. Before using X-ray diffraction, a soil sample is crushed into a very fine powder. The powder is then tested, and as the X-ray is deflected, it produces a pattern on a film. Each mineral and chemical produces a specific pattern. The pattern produced by the sample allows scientists to determine the mineral composition of the soil. Scientists compare the patterns produced by samples taken from a suspect to those taken from a specific location.
Evaluate Ask students where they would look for soil on a vehicle. Also, ask what factors might make using soil stuck to vehicles a tricky task.
SUMMA R Y
Evaluate Have students compare and contrast collecting soil samples with collecting fingerprints at a crime scene.
• Soil taken from crime scenes, victims, and suspects has been used to solve crimes since the late 1800s. • There are three grain sizes of soil: clay, silt, and sand.
• Soil forms in layers called horizons. Starting from the layer at Earth’s surface and moving downward, the horizons are labeled the O horizon, the A horizon, the E horizon, the B horizon, the C horizon, and the R horizon.
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• There are three subcategories of soil: peat, loam, and chalk.
• The pH scale is used to measure how acidic or basic soil is. A pH from 0 to 6 is considered acidic. A pH from 8 to 14 is considered basic. A pH of 7 is considered neutral. • Sand is formed when weathering breaks up rock into small grains from 0.05 mm to 2 mm in diameter. • There are four main types of sand: continental sand, volcanic sand, skeletal sand, and precipitate sand. • There are special procedures crime-scene investigators must follow when collecting soil evidence. • Soil analysis can involve macroscopic and microscopic examination, chemical testing, and X-ray diffraction analysis.
X-ray powder diffraction (XRD) is an instrumental technique used to identify minerals in soil. In the past, XRD was not used extensively because of the expense of the equipment involved and the need for a trained individual to read the results. The same principle used to analyze minerals in soils is also used to analyze building materials, paints, and cosmetics.
Evaluate
CASE S T U DIES
Organize students into groups of two to four and have them read the case studies together. Then, ask them to compare and contrast where soil was found, how the pieces of each case were put together, and how the soil evidence was used to prove guilt in each case study.
Andreas Schlicher (1908) Georg Popp investigated the murder of Margaethe Filbert, who was found in a field in Bavaria, Germany. Neighbors considered a man named Andreas Schlicher to be a possible suspect. Schlicher denied having anything to do with the crime and denied walking in the field where the murder occurred on the day the crime was committed. Police determined that Schlicher’s wife cleaned his dress shoes the night before the murder and that he had worn those shoes only on the day of the murder. The shoes were covered with particles of soil. Popp collected soil samples from the crime scene and also from the area immediately surrounding Schlicher’s home. Popp also collected soil from a nearby castle where clothing and ammunition belonging to Schlicher were found. Soil Examination
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Explore
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Differentiated Learning Teaching Gifted Students Interested students may want to research the uses of XRD. For example, using XRD analysis, it is possible to identify the mineral components in a lipstick smear and potentially identify the manufacturer of the lipstick.
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2 3
Enrique “Kiki” Camarena (1985)
1
Enrique Camarena, an undercover agent for the U.S. Drug Enforcement Agency, infiltrated drug dealings in Mexico and successfully helped destroy millions of dollars of illegal drugs. One of the drug trafficking groups under his investigation identified him as an agent. On February 7, 1985, Enrique and his pilot, Alfredo Zavala, were kidnapped in Guadalajara, Mexico, and killed. They were reported to have been killed by drug dealers during a shootout between Mexican police and the drug dealers. Soil samples taken from the two bodies were found to contain an unusual combination of minerals and volcanic particles. Investigators used this evidence to prove that the men’s bodies were originally buried in the mountains, far away from the shootout. The soil evidence, along with other evidence, eventually showed that the Mexican federal police had been involved in the murders.
4 5 6 7 8
Janice Dodson (1995)
9
John B. Dodson died while on a hunting trip with his new wife, Janice. John appeared to be the victim of a hunting accident. Janice was standing in a nearby, muddy field when John was shot. She returned to their campsite and removed her muddy overalls before getting help for her wounded husband from some men who were hunting nearby. Police determined that John was shot with a .308 caliber firearm, but no weapon was ever recovered. They did find two shell casings by a nearby fence. At the time of the shooting, Janice’s ex-husband was staying at a campsite nearby. He reported that his .308 rifle and some cartridges were stolen from his tent. The ex-husband had an alibi for the time of the shooting, and the case went unsolved for three years. In 1998, investigators returned to the area where John had been shot. They noted that the campsite where Janice’s ex-husband had camped was next to a small pond. The investigators found bentonite, a mineral used to filter larger particles from the water, had been added to the pond water. This means that the mud next to the pond would also contain bentonite, and would be very different from mud taken anywhere else in the area. They reexamined the mud from Janice Dodson’s overalls and found that it was a match to the sample containing bentonite taken from near the pond. This exposed Janice’s lie about her location at the time of the shooting and placed her at the site of the stolen shotgun. Janice Dodson was tried and found guilty of her husband’s murder. She is now serving a life sentence for her crime.
10 11 12 13 14 15 16 17
Think Critically How can layers of soil found on a suspect’s shoes show a sequence of where the suspect has traveled? 348
Soil Examinat Examination
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348
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On the board or overhead projector, list the type of soils. Organize students into groups and assign each group one of the soils. Have the group describe the soil as a forensic expert would.
CHAPTER
Close
When he examined the suspect’s dress shoes, Popp noted three different layers of mud. The layers in the mud told him the sequence of Schlicher’s travels on the day of the murder. In all three layers, Popp successfully compared the material on the shoe with soil from areas near the suspect’s home, the crime scene, and the castle. Schlicher claimed he had walked in his own fields and was nowhere near the crime scene or the castle. His shoes told a different story. He had lied about his travels that day. The dirt on his shoes told more than any information police could obtain from an interrogation.
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Careers
Forensic geologists use earth science and geologic materials, such as soil and rocks, to help solve criminal and civil cases. To become a forensic geologist, you would have to take college-level courses in geology, mathematics, chemistry, law, and forensic science. Some laboratories that employ forensic geologists include the FBI Laboratory in the United States, La Polizia Scientifica in Italy, the Centre of Forensic Sciences in Toronto, and the National Institute of Police Science in Japan. Forensic geologists work in areas other than law enforce- Forensic geologist working in the field. ment. They can also help authenticate a work of art, see if they came from the same source. For such as a painting, by identifying the amount of example, how does the soil on the suspect’s mineral or organic material used to make the shoe compare with the soil type collected at the paints. This information can be used to tell when crime scene? the painting was painted and possibly by whom. A new, developing area of forensic geology is Forensic geologists are hired to test the soil in intelligence work. A person may claim to have and rocks in an area being sold as a mine. The never been to a particular location, but soil and results of their tests provide information on rock evidence from that area is found at the whether that area will be a good source of gold, person’s home. This evidence would link the silver, oil, and so forth. A forensic geologist can person to a specific geographic location. also examine precious stones to determine their Remember the rocky background behind Osama worth before purchase. bin Laden in a tape played on television after Forensic geologists also play a critical role September 11? Where was that tape filmed? in criminal investigations. They can tell if the If that question could be answered, bin Laden’s soil on a body matches the soil at the location whereabouts could be found. John Shroder, where the body is found. If it does not, they a geologist who had done field work in the can help identify the area from where the body area, was able to identify the region where bin was moved. Forensic geologists can compare Laden had been sighted in Afghanistan in two soil samples, one collected from the suspect 2001. and the other collected from the crime scene, to
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Forensic Geologists
Another potential use of forensic geology is in the investigation of wildlife crimes. Illegal specimens of endangered or imported animals and plants might have traces of soil on them that could be linked to a specific locale. The National Fish and Wildlife Forensic Laboratory, the only forensic lab dedicated solely to wildlife crimes, is located in Ashland, Oregon. Suggest that students go to www.lab.fws.gov/index .html for more information.
Learn More About It To learn more about careers in forensic geology, go to school.cengage.com/forensicscience. Soil Examination
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CHAPTER
Chapter 12 Review
CHAPTER 12
True or False 1
1. 2. 3. 4. 5.
False True True False False
Multiple Choice
REVIEW
True or False
2 3 4
1.
Clay particles are larger than sand. Obj. 12.1 and 12.2
2.
Humus is decayed organic material. Obj. 12.2
3.
The R horizon is composed of solid rock. Obj. 12.2
4.
Acidic soil has a pH between 8 and 14. Obj. 12.3
5.
Small, round grains are considered a characteristic of immature sand. Obj. 12.2
6.
Oolites are characteristic of Obj. 12.2 a) continental sand b) volcanic sand c) skeletal sand d) precipitate sand
7.
In which soil horizon would you expect to find a carrot growing? Obj. 12.1 a) A horizon b) E horizon c) B horizon d) C horizon
8.
Which soil type would be best for gardening? Obj. 12.1 a) sand b) loam c) clay d) chalk
9.
A forensic scientist examines a soil sample using a microscope. She finds small, rounded grains made up of quartz crystals. There are also small bits of coral present. From this information, what can you conclude about the origin of the soil? Obj. 12.3 and 12.4
5
Short Answer 9. The small bits of coral would indicate skeletal sand. Skeletal sand made up of coral occurs only in tropical regions. The rounded quartz crystals would indicate continental sand. Also, sand with a high percentage of quartz indicates very old sand. The small, rounded nature of this sand would also indicate its maturity. 10. At a crime scene, investigators must follow certain procedures for collecting, labeling, and packaging soil evidence: • Document all samples by taking photographs. • Sketch the crime scene. • Collect all samples as soon as possible. • Collect surface baseline samples and samples that appear different. • Collect at least four tablespoons of material from several locations. • Package items that have soil attached to them instead of trying to remove the soil. • Carefully remove soil from vehicles and package the soil samples separately. • Collect additional soil samples from the four compass points within a few feet of the crime scene. 350
6 7 8 9 10 11 12 13 14
Short Answer
15 16
_____________________________________________________________ 17
_____________________________________________________________ 10. You are sent to collect soil evidence from a house that has been burglarized. Briefly describe how you would go about collecting samples. Obj. 12.4 _____________________________________________________________ _____________________________________________________________
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Multiple Choice 6. d 7. a 8. b
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11 Answers will vary. Soil evidence in your story can be found on sneakers or embedded in tire treads, tire wells, and in truck beds. Unique soil types might include the soil used on baseball diamonds, gardener’s potting soil, or beach sand. 12. Characteristics might include soil particle size, amount of organic material, moisture content, mineral composition, and soil type.
11. Write a short story of a fictitious crime and describe how soil evidence helped link a suspect to the crime scene or victim. Obj. 12.4 _____________________________________________________________ _____________________________________________________________ 12. Describe physical characteristics of soil that could help distinguish three different soil samples. Obj. 12.1 and 12.3 _____________________________________________________________ _____________________________________________________________
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Bibliography Books and Journals Lee, Henry. Physical Evidence in Forensic Science. Tucson, AZ: Lawyers & Judges Publishing, 2000. Lerner, K. Lee, and Brenda Wilmot Lerner. World of Forensic Science. Belmont, CA: Thomson Gale, 2005. Murray, R. C., Tedwow, J. C. F. Forensic Geology: Earth Science and Criminal Investigation. New Brunswick: Rutgers University Press, 1975. Murray, R. C., Tedwow, J. C. F. Forensic Geology. Englewood Cliffs: Prentice Hall, 1992. ________. “The Geologist as Private Eye.” Natural History Magazine, February 1975. ________. Soil in Trace Evidence Analysis. Proceedings of the International Symposium on the Forensic Aspects of Trace Evidence 1991: 75-78. ________. “Devil in the Details, The Science of Forensic Geology.” Geotimes February 2000; 14-17. Murray, Raymond. Evidence from the Earth. Missoula, MT: Mountain Press Publishing, 2004. Stewart, Melissa. Soil. Portsmouth, NH: Heinemann Library, 2002. Tarbuck, Edward J., Frederick K. Lutgens, and Dennis Tasa. Earth: An Introduction to Physical Geology, 8th ed. Upper Saddle River, NJ: Prentice Hall, 2005. Web sites Gale Forensic Sciences eCollection, school.cengage.com/forensicscience. FBI Handbook of Forensic Services, Revised 2003, www.fbi.gov/hq/lab/handbook/intro.htm. http://query.nytimes.com/gst/fullpage.html?res=9402E5DC123BF930A25751C0A962948260&sec =health&spon=&pagewanted=1 Hayes, Robert A. Forensic Geologists Uncover Evidence In Soil And Water http://www.geoforensics .com/geoforensics/art-1101a.html.
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ACTIVITY 12-1
ACT IV IT Y 1 2 - 1
Ch. Obj. 12.2
EXAMINATION OF SAND (Modified from original lab by Mary Farina)
Background
Objectives:
In this activity, students work in pairs to examine, analyze, and compare various sand samples to determine if they have a common origin and composition.
By the end of this activity, you will be able to: 1. Examine and compare various samples of sand. 2. Compare and analyze samples and determine if they have a common composition and origin.
Time Required to Complete Activity:
Safety Precautions
(students working in pairs) stereo microscope or hand lens sand samples from five suspects and the crime scene microscope slides sieve set (to share with other groups) dropper bottle of dilute hydrochloric acid (0.1 M) small paintbrush teaspoon or other small measuring device
Safety Precautions: Goggles should be worn when working with dilute hydrochloric acid. Materials should be discarded as directed by your instructor.
Procedures
352
Sand from Vero Beach, Florida.
Five suspects were identified in a theft involving stolen property from a beach house. The suspects’ shoes were confiscated, and the sand found was compared to that at the beachfront property. Sand from differing locations may be unique in appearance. Microscopic examination can tell a great deal about the origin, composition, and age of the sample of sand.
Procedure: 1. Using a stereo microscope or hand lens and slide, examine 50 grains of sand of Sample 1. 2. Describe your results on Table 1. Include the source of the sample indicated on the container and the type of crystals, fragments, or both if present. Crystals consist of one type of mineral only. Fragments consist of two or more minerals. 3. While viewing the 50 grains under the microscope, determine how many quartz, feldspar, black minerals, and others are in the count of 50 grains. Multiply each number by two to determine the percentage. 4. Examine the sand for degree of rounding. Degree of rounding can be either very round, rounded, or angular edges.
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7. Sand samples must all be dried before comparisons are made.
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Background:
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Materials:
1. Print, copy, and distribute Activity Sheet 12-1 from the IRCD. 2. Emphasize that safety goggles should be worn when working with dilute hydrochloric acid. An eyewash should be available in case of an accident, and students should know how to use it. 3. Remind students to use both hands to carry a microscope. 4. Instruct students on how to discard all materials.
1. Make sure students read all directions before beginning the activity. 2. If you have one, a stereomicroscope will allow students to view the sand samples in three dimensions. 3. Regular microscope slides will not work very well for this activity because you cannot drop a coverslip on top of sand. Depression slides work much better, especially if slides are to be viewed with a compound-light microscope. 4. Make sure the sand samples are labeled, and remind students not to mix up the samples. 5. Instead of using 50 grains of sand, it might be easier to have students use a teaspoonsize measuring spoon. 6. Provide a small bucket for students to wash the sand from the slides, instead of dumping the sand into the sink.
45 minutes
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5. Use the sieve stack to separate a teaspoon of the sample and determine which sieve has collected the fragments. Record as either most, some, least, or none. This will give you an approximate idea of the percentage of particle size in the sample. View each sieve and compare which sieve has collected the most, some, least, or no particles. 6. Add a drop of hydrochloric acid to your slide of sand grains. Bubbling indicates the presence of carbonates, the shells and skeletons of dead marine organisms. Record if bubbling occurred and to what degree. 7. Wash off the slide. 8. Repeat the process with each of the other Samples 2 through 5. 9. Repeat the process for the Crime Scene sample (beachfront area). Determine if the soil from the crime scene matches any of the samples taken from the suspects.
Answers Check students’ data tables.
Questions 1. Answers will vary. Students will have an absolute match if the unknown sample was taken directly from the known sample. If these samples were collected separately from each other and on different days, there will not be an absolute match because of environmental changes over time and samples not taken from exactly the same place. 2. Answers will vary. Students should mention that soil evidence is just one type of trace evidence found at a crime scene. If this evidence matches a suspect to the crime, it is only one piece of the puzzle. Investigators will need more information to develop a clear picture as to what happened.
Data Table 1: Comparison of Sand Analysis
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Characteristics Source of sand Crystals or fragments or both Minerals found per 50 grains: Quartz—————— Feldspar————Black minerals— Other——————Rounding: Very rounded, rounded, or angular edges Particle size: record as most, some, least, or none Top sieve (4 mm) 4th sieve (2–3.99 mm) 3rd sieve (0.25–1.99 mm) 2nd sieve (0.062–0.249 mm) Bottom sieve (≤0.062 mm) Reaction with hydrochloric acid: Bubbles and sand totally dissolves or bubbles slightly or does not bubble at all
Sample 1
Sample 2
Sample 3
Sample 4
Sample 5
Crime Scene
% of total ______% ______% ______% ______%
% of total ______% ______% ______% ______%
% of total ______% ______% ______% ______%
% of total ______% ______% ______% ______%
% of total ______% ______% ______% ______%
% of total ______% ______% ______% ______%
__________ __________ __________ __________ __________
__________ __________ __________ __________ __________
__________ __________ __________ __________ __________
__________ __________ __________ __________ __________
__________ __________ __________ __________ __________
__________ __________ __________ __________ __________
Questions: 1. Your unknown sample appears closest to which sand sample? Is it an absolute match? Why or why not? Justify your answer from the data collected from your soil examination. 2. Would matching sand evidence from a crime scene to a suspect be enough evidence to convict a suspect of a crime? Explain your answer.
Soil Examination
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Further Research and Extensions An alternate way to examine samples in this lab is to put the sand samples into glass or plastic Petri dishes and use a stereomicroscope capable of viewing up to 40X. Use both the top and bottom lights of the stereomicroscope.
353
ACTIVITY 12-2
ACT IV IT Y 1 2 - 2
Ch. Obj. 12.1, 12.3, and 12.4
SOIL PROFILE EXAMINATION
Background
Objective:
In this activity, students study soil characteristics and match samples taken from a suspect to samples found at a crime scene.
By the end of this activity, you will be able to: Study soil characteristics and match samples taken from a suspect to samples found at a crime scene.
Time Required to Complete Activity: 60 minutes over two consecutive days
Safety Precautions
(to share by teams of four) 5 hand lenses or compound microscopes or stereomicroscope with 40x magnification 5 graduated cylinders, 250 mL 5 soil samples, four from suspects and a crime scene sample 5 rubber bands 5 beakers, 250 mL 5 pieces of cheesecloth approximately 8" x 8" 5 teaspoons 5 pieces universal range pH paper 5 watch glasses 5 ultraviolet lights 5 flat toothpicks
Procedures 1. Print, copy, and distribute Activity Sheet 12-2 from the IRCD. 2. Make sure students read all directions before beginning the activity. 3. Some students may need help with adjectives and other descriptors for color, texture, and odor. Discuss this in advance of completing the activity to avoid getting ambiguous data recorded, such as “smells like dirt.” 4. Make sure that all students use the same spoonful measurement, because standardization of sample size is important to obtaining data that can be compared among lab groups. 5. Before beginning the activity, discuss why it would be an improper lab technique to not use standardized samples, volume of water, and soaking time.
354
Safety Precautions: Proper eye protection is needed for the UV light.
Background: A robbery has occurred, and four suspects have been questioned. Soil samples were taken from the wheel wells of each of the suspects’ vehicles. Do any of the soil samples match soil from the crime scene?
Procedure: Part A: Microscopic Examination Obtain four soil samples (1 to 4) and a crime scene sample. 1. Examine a dry Soil Sample 1 (from Suspect 1) using a hand lens or low power (40x ) on a microscope. Because soil changes somewhat in appearance as it dries out, make sure each sample is dry before beginning your examination. 2. Record all information requested on Table 1 on page 355. 3. Describe or sketch any organisms found in the soil. 4. Describe the color, texture, odor, and overall appearance of the soil.
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Materials:
1. Students must wear proper eye protection when using the UV light. 2. Remind students to use both hands to carry a microscope.
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Teaching Tip
Data Table 1: Soil Analysis Describe or sketch any organisms or Soil foreign objects Sample found
Color of Dry Sample (black, brown, gray, etc.)
Sample Texture (crumbly, gritty, loose, sticky)
Odor of Sample (smells like ? or no odor)
Overall Appearance of Sample (sandlike, organic, rocks, minerals)
If time is an issue, divide lab procedures between partners in a group.
Appearance under UV Light (glows, no glow)
1 2 3
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4 Crime Scene
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Part B: UV Examination 5. View the sample in a darkened room using a UV light and describe what you see. 6. Repeat the procedure and examine each of the other suspect samples and the crime scene sample. Part C: Determination of pH of the Soil Sample The pH value is a measure of whether something is acidic, neutral, or basic. 7. Place a piece of cheesecloth on a clean surface. Place two spoonfuls of soil from Sample 1 in the center of the cheesecloth. Gather the sides of the cheesecloth and place a rubber band around the cheesecloth, capturing the soil sample in a ball within the cloth. 8. Place 50 mL of distilled water in a 250-mL beaker and label it Suspect 1. 9. Place the ball of soil in the water and leave it undisturbed for 10 minutes. 10. Repeat steps 7 to 9 for suspect samples 2, 3, 4, and the crime scene sample. Let samples sit for 10 minutes. 11. Using the pH paper, determine the pH of the water for each of the soil samples and complete the chart. If the pH value is less than 7, the soil is acidic. The lower the number, the more acidic. If the pH equals 7, the soil is neutral. If the pH is greater than 7, the soil is basic. The higher the number, the more basic the sample. 12. Record your results on Table 2 on page 356. Part D: Sedimentation of Soil Samples Soil samples that seem identical can be further examined by creating a sedimentation column. As shaken materials separate, they will layer, with the densest materials settling to the bottom first. 13. Into a 100-mL graduated cylinder, add one heaping teaspoon of Soil Sample 1. 14. Cover the top of the cylinder; shake the contents for 30 seconds. 15. Repeat steps 13 and 14 for each of the other samples.
Soil Examination
355
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355
Answers Check students’ data tables.
Data Table 2: pH Determination Soil Sample
pH
Acidic or Basic?
pH Paper
1
1. Answers will vary. 2. Sample answer: Expert testimony could be given in a court of law describing the sample evidence and how closely the sample found on the suspect matches what is found at the crime scene. 3. Answers will vary. Sample answer: X-ray diffraction allows scientists to identify the mineral makeup of a soil.
2 3 4 Crime Scene Data Table 3: Soil Sedimentation Results Sample Using colored pencils, draw a sketch to scale of the layers in the column
1
2
3
4
Crime Scene
Number of Distinct Layers Description of Floating Material
16. Allow all samples to settle overnight and compare the overall appearance of each sample. Note any floating material in your description. 17. Record your results in Table 3.
Questions: Compare your results from Parts A to D of this activity. 1. The crime scene sample and sample ____ is a match. Justify your results. 2. How could they be used in a court of law? 3. Research what other types of analysis might be performed to compare soil samples.
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Further Research and Extensions Sometimes soil evidence has maggots in it. Interested students may want to combine what they learned about insect evidence and soil evidence and research cases that used these two kinds of evidence.
356
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Questions
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A C T IV IT Y 12- 3
AC TIVITY 12-3
Ch. Obj. 12.2 and 12.4
CHEMICAL AND PHYSICAL ANALYSIS OF SAND
Background
Objectives:
In this activity, students examine and compare chemical reactions and the magnetic and fluorescent properties of sand samples. Students also compare samples and determine if there is a match between sand found on a crate of narcotics and sand from four possible ports of origin.
By the end of this activity, you will be able to: 1. Examine and compare chemical reactions in various samples of sand. 2. Examine and compare the magnetic and fluorescent properties of sand. 3. Compare samples and determine if there is a match between sand found on a crate of narcotics and sand from four possible ports of origin.
Time Required to Complete Activity: two periods, 45 minutes each
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Materials:
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(students working in pairs) 1 dropper bottle of acetic acid (0.1 M CH3COOH) 1 dropper bottle of dilute hydrochloric acid (0.1 M HCl) 1 dropper bottle of silver nitrate (0.1 M AgNO3) 5 sand samples numbered location 1 to 4 and a crime scene narcotics crate 5 microscope depression slides (if available), or 5 watch glasses, or a well plate tray with 15 wells magnet 5 flat toothpicks UV light (to share with other groups) 5 squares of black paper, 3" x 3"
Safety Precautions 1. Emphasize that students must wear safety goggles to protect their eyes from harmful solutions and from UV light. 2. Remind students to use both hands to carry a microscope. 3. Instruct students as to the proper way to handle and discard all materials. 4. Caution students that silver nitrate solution will stain clothing and skin. 5. Tell students never to look directly into a UV light source!
Safety Precautions: Goggles are to be worn to avoid contact between harmful solutions and your eyes. All materials are to be handled as described by your instructor and discarded as directed. Silver nitrate solution will stain clothing and skin temporarily. Avoid looking directly into a UV light source. Proper eye protection is needed for the UV light source.
Background: Customs officials from New York City noted the presence of sand in a crate containing narcotics. The sand was analyzed and found to be composed of quartz, feldspar, and shell fragments from a high-energy beach (a beach with lots of wave action). In an attempt to trace the route of the narcotics, a list of all ports visited by the ship was obtained. Samples of sand were obtained from each of the four possible ports and compared to the sample carried with the narcotics. The smugglers were later apprehended and arrested.
Soil Examination
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Reactions to Be Examined: 1. Test for sulfates: sample sulfates + BaCl2 + CH3COOH ➝ BaSO4 (a white precipitate) + dissolved materials sample sulfates + barium chloride + acetic acid react to form ➝ a white solid 2. Test for chlorides: sample chlorides + AgNO3 + CH3COOH ➝ AgCl2 (a white precipitate) + dissolved materials sample chlorides + silver nitrate + acetic acid react to form ➝ a white solid 3. Test for carbonates (living material): sample carbonates + HCl ➝ CO2 (gas bubbles) + H2O + dissolved materials sample carbonates + hydrochloric acid react to form ➝ gas bubbles of carbon dioxide
Procedures
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1. Print, copy, and distribute Activity Sheet 12-3 from the IRCD. 2. Make sure students read all directions before beginning the activity. 3. Silver nitrate is an expensive reagent, which can stain clothing and skin even in low concentrations. Handle it with care, dispensing from polyethylene dropper bottles. Make sure there is money in the budget to buy this solution. 4. Suggest to students that they slide the magnet underneath the plastic well plate or watch glass. If they place the magnet directly in the dirt, it will work, but the soil particles will be difficult to remove from the magnet. This test works best when the soil is dry. 4. Students can either use about 150 grains of sand or about ½ teaspoon.
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Procedure:
Chloride Test 6. Place about 50 grains of the Location 1 sample in a depression slide and add two drops of the 0.1 M silver nitrate solution and two drops of the 0.1 M acetic acid solution. 7. Stir with a toothpick and observe under a hand lens or microscope on low power. If a white precipitate forms, chlorides are present in the sand sample. 8. Record your results on Table 1. 9. Repeat steps 6 to 8 for each of the other sample locations and record the results on Table 1. 10. Wash off all of the slides and prepare for the carbonate test. Carbonate Test 11. Place about 50 grains of the Location 1 sample in a depression slide and add two drops of the 0.1 hydrochloric acid solution.
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Soil Examination
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© Cengage Learning. All rights reserved. No distribution allowed without express authorization.
A small scoop of soil is all that is needed for an analysis.
©J. Beam Photography
Sulfate Test 1. Place about 50 grains of the Location 1 sample in a depression slide and add two drops of the 0.1 M barium chloride solution and two drops of the 0.1 M acetic acid solution. 2. Stir with a toothpick and observe under a hand lens or microscope at low power. If a white precipitate forms, sulfates are present in the sand sample. 3. Record your results on Table 1. 4. Repeat steps 1 to 3 for each of the other sample locations and record the results on Table 1. 5. Wash off all of the slides and prepare for the chloride test.
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12. Observe under a hand lens or microscope. If bubbles form, carbonates are present in the sample. 13. Record your results on Table 1. 14. Repeat steps 11 to 12 for each of the other sample locations and record the results on Table 1.
Answers Check students’ data tables.
Questions
Magnet Test 15. Using a magnet, determine if any of the samples contain any magnetic components. 16. Record on Table 1.
1. Answers will vary. 2. Sample answer: The shape and age of the sand samples could be studied.
Fluorescence Test 17. In a darkened area, determine the fluorescence of each sample of sand. The UV light will cause fluorescent material to glow. 18. Sprinkle a small amount of Location 1 sand on a piece of black paper and observe it under UV light. 19. Record the size, shape, and percentage of fluorescent particles on Table 1. 20. Repeat steps 18-19 for the other samples.
© Cengage Learning. All rights reserved. No distribution allowed without express authorization.
Data Table 1: Sand Testing Results Beach Sand Sample Location
Sulfate Test (white ppt, yes or no?)
Chloride Test (white ppt, yes or no?)
Carbonate Test (bubbles, yes or no?)
Magnetic UV Reaction: Fluorescence Particles (yes or Size Shape % of no?) Particles
1
2
3
4
Narcotics Crate
Questions: 1. 2.
Based on the comparison of results in Table 1, can you match a location to the beach from which the drugs were transported? Describe additional testing of the sand samples that would provide further evidence for a possible match. Justify your answer.
Soil Examination
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Further Research and Extensions A challenging extension to this lab would be to prepare an unknown mixture of two of the sand types and have students not only determine which two were mixed, but also in what proportions.
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