A Lab Demonstration: Three dimensional view of soft internal structures of bony material
photo: Andrew MacRae


Author:
Steve Miller, Kromery Middle School, Middleton, WI


Grades:
7-12


Suggested Time:
This demonstration needs to be set up one day and then explained a day later.


Students' Prior Knowledge:
Ask the students the following questions: What does the interior of a bone look like? Do bones inside the body appear like the white skeletons seen in biology class? What is preserved during the fossilization process? Is there any "real" bone left?


Background Information:
Bone is not just white brittle material that snaps like a twig when put under strain. A typical long bone has two types of bone, a strong outer layer called compact bone and a soft porous center called spongy bone. Both compact and spongy bone are interlaced with blood vessels supplying the cells of the bone.

Bone is a composite material made of:
1. Hydroxyapatite: is an inorganic mineral composed of calcium phosphate and water. Hydroxyapatite is a hard, brittle, and rigid material which gives the bone its structural strength. (Bone is 80 - 90% hydroxyapatite)

2. Collagen: is the organic part of the bone, and is made of many types of protein. Collagen gives the bone its flexibility and is both soft and strong. (Bone is 10 - 20% Collagen)

3. Soft Tissue: Blood vessels, nerves and marrow core. Supply the bone with stimuli and nutrients.

When a bone becomes a fossil, the hard compact bone, soft spongy bone and spaces inside the bone such as nerves, blood vessels and marrow core can be preserved, but often in different ways.

Permineralization is a type of preservation where the soft organic material of the bone decomposes and leaves empty spaces inside of the bone. These spaces where the nerves , blood vessels and the marrow core once resided can become filled in with minerals such as silica, calcite, iron pyrite, and limestone transported by ground water.

There is usually a chemical difference between the bones and the material that has filled in the soft parts of the bone via ground water. These chemical differences allows you to dissolve the outer bony material (hydroxyapatite) in HCl acid leaving the silicates material that has filled in the blood vessels behind. This allows the three dimensional structure of the bones interior structures to be seen.


Lab Demonstration:
Three dimensional view of soft internal structures of bony material.


Materials:

• HCl acid small beaker binocular dissection microscope * small piece of permineralized dinosaur bone safety goggles
• gloves or forceps

* The piece of dinosaur bone needed for this demonstration is relatively common. It can be purchased at a rock and mineral store as just a scrape piece of dinosaur bone. It does not have to be pretty or shaped anything like a recognizable piece of the overall skeleton. This type of scrape bone can be purchased for $.50 a piece at my local rock shop. Dinosaur bone preserved with silicates is one of the most common types of permineralization. Be careful not to purchase bones that have been preserved with iron pyrite or limestone derivatives.

1. Using a piece of bone that has been permineralized with silica, hold one end of the bone suspended in a beaker of HCl acid (6 M). The bone (hydroxyapatite) around the silica will react leaving the silica behind. Let the bone sit in the acid for several hours. Wash off carefully and set aside to dry.

2. Carefully place the bone under a dissection binocular microscope. Do not let the side that was in acid touch any surface, so that the delicate surface is not destroyed.

3. Focus the microscope on the end of the material that was in the acid. What is seen is the three dimensional pattern of blood vessels that have been filled in by silicates.



Teacher Notes:
Two common types of bone preservation is permineralization and replacement. What happens chemically to a bone when it is preserved can be very different depending on the environment of preservation.

Permineralization is a type of preservation where the soft organic material of the bone decomposes and leaves empty spaces inside of the bone. These spaces where the nerves , blood vessels and the marrow core once resided can become filled in with minerals such as silica, calcite, iron pyrite, and limestone transported by ground water.

Replacement occurs when the hydroxyapatite (calcium phosphate) of the bone is replaced by atoms suspended in the ground water around the bone. For example the calcium atom in the bone can be replace by an atom of strontium, barium, lead, or another calcium atom.

The word fossil means: evidence of life from the past. This is a very general term and can be applied to many different types of material from the earth¹s past including: trace fossils, molds, casts, impressions, and skeletal parts.

Biology: A biology student could use this demonstration to visualize the inner structure of a bone and try to determine the types of soft tissue that is being observed. There is no way to make these types of observations in modern materials.

Earth Science: An earth science student could use this activity to look at the crystal structure of the silicate preservation. What are different types of preservation like and how can knowing the chemical properties of preservation help understand the environment necessary for a fossil to be preserved.


Wisconsin State Science Standards:
F.8.6
http://www.dpi.state.wi.us/standards/scif8.html
Explain* how some of the changes* on the earth are contributing to changes in the balance of life and affecting the survival or population growth of certain species.

F.12.2
http://www.dpi.state.wi.us/standards/scif12.html
Analyze* the geochemical and physical cycles of the earth and use them to describe* movements of matter.