History of Shells

Introduction: (Initial Observation)

In this project you will learn about shells as well as their chemical structure and some of their physical properties.

Information Gathering:

Gather information about shells and their origin. Find out where they come from, how many varieties exist and why they are important. Read books, magazines or ask professionals who might know in order to learn about the uses of shells.
Keep track of where you got your information from. The following are samples of information that you may find.

The varieties of shells found on the shores of the sea, in the forests, and along the banks of lakes and rivers are simply stone “forts” that soft-bodied mollusks and other animals build around themselves for protection. Shells are composed of substances secreted by the glands of the mollusks. They consist largely of carbonate of calcium, which is the basic ingredient of limestone, and marble.
As a mollusk grows, so does its shell. The lines of growth are usually clearly marked by the ridges that run parallel to the outer, or free, edge of the shell. These are clearly visible in the shells of oysters and clams. The other ridges and bumps on a shell are caused by corresponding projections on the mollusk’s mantle (the soft lining between the animal’s body and its shell).

How many different kinds of shells are there?

There are between 50,000 and 200,000, species of mollusks, depending on whose doing the counting. These figures are based on the number of species that have been described, and which of those the count accepts as valid, and the estimates of the number of undiscovered and undescribed species remaining on earth.

Why are there so many different shapes of shells?

Mollusks’ shapes are a product of heredity combined with habitat and life style for the most part. Shell shapes have evolved to make their lives easier. A snail that burrows through sand needs a shell that will move through wet sand easily — the best kind of shell is a smooth, slender, gradually tapering, narrow end at the front, with no impeding projections, but mollusks have worked out many variations on this theme. A shell that needs lots of camouflage may have evolved a spiny or irregular surface, which will catch and hold all sorts of camouflaging encrusting organisms. Spines are also helpful for discouraging predators and, in some arrangements, for life on mud…broad weight distribution.

How big do shells get?

The biggest marine snail is Syrinx aruanus, the Australian Trumpet, at 77.2 cm. (over 30″). The biggest American marine snail, the Horse Conch, Pleuroploca gigantea, is just over 2′. The world’s biggest clam is of course the reknowned Giant Clam of the southwest Pacific, Tridacna gigas. The largest one on record, in the American Museum of Natural History, measures in at almost 55″. (Incidentally, their favored diet is not divers but algae they farm within their own bodies.) These sizes are taken from Wagner and Abbott’s World Size Records, published by American Malacologists and edited by Barbara Haviland of St. Petersburg, Florida.

Source…

Question/ Purpose:

What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.

Any of the following can be a question for this project.

1. What are the chemical properties of shells?
2. What is the rate of reaction of Vinegar and shells? (Experiment 1)
3. How many different types of shells exist in the world?
4. Do shell types vary based on geographical areas?
5. How old can a shell fossil be?
6. Can we identify a mollusk based on its shell?
7. Why do you hear sound from the shell? (Vibration or reflection) (Experiment 2)
   Do shells have any industrial application?

Identify Variables:

When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.

For a general study of shells, there is no need to define variables. In more advanced research on shells, you may consider many different factors such as climate, elevation, type of water and anything else that may affect the life of mollusks as a variable. Then you can see how these variables affect the type or population of mollusks who produce shells.

This is how you define variables for question 2 (Experiment 1)

Independent variable (manipulated variable) is the time shells are in vinegar.

Dependent variable (responding variable) is the rate of reaction.

Controlled variable is temperature.

Hypothesis:

Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis.

A general study on shells, their varieties and distribution does not require a hypothesis. If you are studying a specific question and you are performing an experiment, then you need to have a hypothesis.

Following is a sample hypothesis for question 2 (Experiment 1).

The rate of reaction of acid and shells increases by time. My hypothesis is based on my observation of the shell samples. It seems that most shells have a protective layer over them and this protective layer may initially protect the shell. I expect the rate of reaction to increase as the top layer of the shell disappears.

This is another sample hypothesis:

The rate of reaction of acid and shell decrease by time. I think initially acid is strong, but the reaction weakens the acid so the rate of reaction will reduce because of depletion of acid.

Experiment Design:

Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”

Experiment 1: What is the rate of reaction of vinegar and shell?

Note for parents: By doing this experiment student will learn that Vinegar is a 5% solution of acetic acid in water. Also, shells in most part are a chemical known as Calcium Carbonate. Acids react with carbonates and release carbonic gas.

Introduction:

Placing a seashell in an acid such as vinegar starts a chemical reaction releasing a gas. Bubbles will form on the surface of the shell and then rise up to the surface. This gas is known to be Carbonic gas (the same gas used in soda drinks and carbonated water). Further studies have shown that carbonic gas is being released because shells in most part are made of Calcium Carbonate (similar to eggshell and marble).

In this experiment you observe the chemical reaction of vinegar and shells. You will also record the rate of reaction.

Procedure:

1. Get 5 identical cups. Label them “Control”, 1, 2, 3 and 4.
2. Add exactly 100 grams of shells to each cup.
3. Add same amount of white vinegar to cups 1 to 4, Level of vinegar must be at least one inch above the level of shells. Do not add vinegar to control.
4. After one hour from the time you added the vinegar remove the remaining shells in cup number 1 and dispose the vinegar in a sink. Wash, rinse, dry and mass the remaining shells.
5. After two hours from the time you added the vinegar remove the remaining shells in cup number 2 and dispose the vinegar in a sink. Wash, rinse, dry and mass the remaining shells.
6. After three hours from the time you added the vinegar remove the remaining shells in cup number 3 and dispose the vinegar in a sink. Wash, rinse, dry and mass the remaining shells.
7. After four hours from the time you added the vinegar remove the remaining shells in cup number 4 and dispose the vinegar in a sink. Wash, rinse, dry and mass the remaining shells.
8. Record the results in a table like this:

To calculate the reaction rate subtract the final mass from the initial mass to calculate the mass of shell consumed by the reaction. Then divide this by the initial mass.

For example if the final mass is 82 grams, then 100-82=18 grams of shell is consumed by the reaction. If you divide 18 by initial mass, the reaction rate will be 0.18 or 18%.

You can finally use the hours and the reaction rate from the above table to draw a graph.

Experiment 2: Why do you hear sounds from the shell?

Introduction:

We hear the sound of the seashore inside large shells. Why do shells make this sound? Some believe it is because the shell echoes surrounding sounds, jumbling and amplifying them. Others believe shell sound is caused by internal vibrations of the shell (resonance). In this experiment I will test to see if the sound of shells is an echo or caused by vibration.

Sample hypothesis:

I think shells echo the sound from the surrounding area because inside the shell is hard and smooth. In other words inside surface of shells reflect the environment sound back to us.

Identifying variables:

The independent variable (manipulated variable) the condition of surface inside the shell (smooth, rough)

Dependent variable (responding variable) is the loudness of the sound from inside a shell.

Procedure:

1. Find two identical shells that you can hear sound echo from them.
2. Use a small marker and label them with “Experiment” and “Control”.
3. Listen to the sound echo from both shells to make sure that they both have the same level of echo.
4. Make a dilute solution of wood glue. Pour it inside the “Experiment” shell and empty it again. Use a brush to remove excess glue.
5. Fill up the “Experiment” shell with starch and empty it again. A layer of starch will remain inside the shell, so inside the shell will not be smooth and reflective any more. Leave it for a few hours to dry.
6. Listen to both shells again.
7. Use the results to draw a conclusion.

How to draw a conclusion?

If the sound from the shell is an echo from the sounds in the environment, then changing inside the shell must stop the sound. A layer of starch is not reflective any more.

If the sound is an internal vibration of the shell (resonance), then you should hear the sound again regardless of presence of starch.

Materials and Equipment:

List of material can be extracted from the experiment section.

Results of Experiment (Observation):

Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.

Calculations:

You need to calculate the rate of reaction for experiment 1.

To calculate the reaction rate subtract the final mass from the initial mass to calculate the mass of shell consumed by the reaction. Then divide this by the initial mass.

Summery of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.

Conclusion:

Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.

References:

All these web sites contain valuable information about shells. You may use them for your project or just review them for fun.
http://www.jaxshells.org/
http://coa.acnatsci.org/conchnet/edutrack.html
http://www.coneshell.net/
http://www.eurasiashells.net/
http://www.seashells-export.com/
http://www.seashellcity.com/
http://web.ukonline.co.uk/conker/fossils/index.htm
http://www.seashells.org
http://ousd.k12.ca.us/~codypren/Sea_shells.html
http://www.shelly.de/
http://www.fossilexpeditions.com/fossil1.htm
http://user.icx.net/~midgard/shells/shells.htm
http://www.seashells-export.com/
http://www.isr.umd.edu/~didier/seashell/ross.html