1.11 Soil 1

Activity 1: The Camarena Case (ONLINE)

Instructions

The Kidnapping and Murder of Agent Camerena

Listen to the story about the U.S. DEA agent named Enrique Camarena. How do you think soil evidence can help resolve this case? Write your ideas below. They identify where the soil comes from to see where the main and or secondary site of the crime is located.

Activity 2: Soil Composition (ONLINE)

Instructions

It’s not dirt. It’s soil.

What is the composition of soil? Soil is a mixture of inorganic material, organic material, water, and air.

  • The organic matter called humus, is the decayed remains of plants and animals.
  • The inorganic material consists of mineral particles of various sizes.
    • the mineral particles are classified by grain size.

 

How do sand, silt, and clay differ? Sand is the largest grain (0.05-2.0mm), Clay is the smallest grain size ( less than 0.002), and Silt is an intermediate size.

  • soils usually have all three grains, but the percentages of those components vary.

 

 

What is loam? Loam is a mixture of sand, silt, and clay in varying proportions.

 

 

 

Not all soils are the same.

What are four properties of soil? Mineral composition

  • types of minerals in soils vary
    • For example, volcanic soils contain volcanic ash and glass. Beach soils may contain high amounts of calcite from marine organism.

Color

  • Soil color depends on many factors. Black soil has lots of organic matter with little or no air. Red soil has oxidized iron which is rust. Blue gray, and olive soils may have a relatively high amount of water.

Smell

  • Red and brown soils may smell sweet, while black soils may smell like rotten eggs.

Texture

  • Soil can feel gritty, flour-like, or sticky. Soil composition determines texture. Ex: Predominantly sand soils are gritty, while clayey soils are sticky.

 

 

 

 \n There is a taxonomy of soils.

How are the taxonomies of soil similar to the taxonomies of living organisms? The use a hierarchy to describe soils.

  • order
  • suborder
  • great group
  • sub group
  • family
  • series

 

How is soil evidence examined?

Complete the sentences.

 

  • The color of soil is determined by using the Munsell scale.

 

  • The size of soil is determined by sifting through a series of sieves.

 

  • The density of soil is determined by weighing a dried, known volume of soil.

 

  • Experienced scientists can identify the type of grain by examining soil under a microscope.

 

 

 \n Soils have layers.

Describe the horizons of soil.

  • Humus is decayed organic material
  • top soil is a dark-colored mixture of humus and mineral particles
  • Subsoil is lightly colored and contains clay and minerals that came down from above.
  • Clay and fragmented bedrock lie on the bedrock.
  • Unaltered bedrock is the parent material that forms soil when weathered.
Activity 3: Soil Impressions (ONLINE)

Instructions

How is soil evidence collected?

Describe four important steps forensic scientists follow when collecting soil samples.

  • Sample immediately before the soil becomes contaminated
  • Get baseline samples at the scene, at compass points a few feet from the scene, and at points 20-25 feet from the scene.
  • Document all samples with sketches and photographs.
  • Store samples properly in leakproof plastic containers, such as film canisters.

 

 

Soil impressions can preserve evidence.

What is a soil impression? prints on the soil left by shoes or tires.

 

 

What material is often used to collect soil impressions? Dental stone