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MAKING SEA-SHELL FOSSILS

It takes nature thousands of years to make a fossil. We're going to make some fossils in just a few days. Of course, our fossils will be fake ones. Some of the people who sell costume jewelry set pieces of glass into metal, and shape the metal into rings. Then they sell "faux diamond rings." (Faux is a French word meaning false, pronounced "fo".) We can call our fossils "faux fossils."

Do you remember that last week I asked you to bring seashells or snail shells to school, and put them into that box on the counter? The box is now almost full, and there are enough shells so that every student has one. Line up, and go to the counter and get a craft tray (if you don't have regular craft trays, the trays that packaged meats come in are good, or even sturdy paper plates). On your tray, place one shell of your choosing, one block of modeling clay that is about twice the size of your shell, one of the small brushes, and one pill-cup of petroleum jelly.

Now that you're back in your seats, using your brush, coat one side of your shell with the petroleum jelly, and press that side of the shell into the clay. Remove the shell and put it aside. Pinch the clay around the outside edge of the block so that there is a little rim to keep the plaster from spilling over the sides. Now, coat petroleum jelly onto your mold--not only into the impression made by your shell, but the entire surface of the top of the block, including the inside edges of the rims you made around the edges. Why do you think we are putting petroleum jelly onto the molds? Same reason we put it onto the shell. So it wouldn't stick.

Your teacher has prepared some plaster of Paris, by following the directions on the package. He or she will come around with it, and each of you may dip out a cupful, to pour into your mold. Pour enough plaster so that there is plaster all the way to the rims, but don't let it spill over. Put your name on your craft trays, and put them onto the counter. They have to dry for 24 hours.

Tick-tock, tick-tock, Good morning!!!

Yesterday, we poured plaster into our molds. They should be dry by now. Each of you may go to the counter and get your craft tray, one small square of fine sandpaper, and a dull craft knife.

Gently remove the rims of clay, and lift the plaster off the clay. Turn it over, and there is your faux fossil! If it has a few rough spots, or bubbles, they can be repaired by sanding, or by scraping carefully with the knife. If there is a really big bubble, we can fill it with a little plaster.

How would nature make fossils that look like this? Sometimes marine organisms who live in shells, such as scallops, oysters, clams, mussels, snails, and others, get buried in the mud, silt, and ooze on the ocean floor. Their bodies die and decay. Their shells eventually dissolve. By the time the shell dissolves, the mud and stuff in which they were buried will have hardened, and the space left by the shell would be just like your clay molds, having the exact shape of the shell impressed in it. Over time, that "mold" would have filled with other materials, sometimes even molten rock (lava) which flows from a magma chamber under the floor of the ocean. The new material would also become hard, and the tide, a whirlpool, or other turbulence (maybe an earthquake) could break the mold loose from the cast (the part of the fossil that is like your plaster cast). Both the mold and the cast would be fossils. Remember, it only takes a few minutes to tell how it happens, but it takes thousands of years for this process to take place.

We can make faux fossils of the whole shell, so that you can see exactly what I just described. Coat the shell with petroleum jelly, and press it into two blocks of clay, using one block for each side of the shell. Separate the clay, and remove the shell, and set it aside. After coating the insides of the mold with petroleum jelly, put the clay blocks together tightly and hold them together with rubber bands. At the top of the blocks, cut a small funnel-shaped hole into the center of the seam, so that your plaster can be poured into the mold made by your shell. Pour in a little plaster, and tap the mold so as to break any bubbles that may have formed in the plaster, then add more plaster. Keep doing that until the mold is full. If plaster leaks from the mold, press the blocks together--pinch the clay with your fingers--so as to stop the leak. Since the surface of the plaster is not exposed to the air, we will wait two days before removing the mold. Tick-tock, tick-tock. Good morning. Bye….

Tick-tock, tick-tock. Good morning! Get your trays!

After removing the mold, do any necessary trimming with the sandpaper and the dull knife. Break off the plaster "hat" left by the funnel through which you poured the plaster. This shows you the kind of fossil that nature gets when it buries a whole shell.

So what? Big deal. So what do we care? Why do fossils make any difference to us?

First of all, please be assured that fossils make a great difference to us, and that they are very important. Now that you know that, each of you can make a list of reasons you think there might be. You can compare your lists with this list:

1. Fossils tell scientists the types and sizes of animals that lived in the distant past;

2. Tests made on fossils tell scientists approximately how long ago they lived;

3. The types of materials in which fossils are found tell scientists the area where the fossil first died, the cooling rates of some different materials, and the times of lava flows, as well as other items of information;

4. Comparing different fossils of the same type, from different areas, tells scientists the times of certain geologic events, such as an ice age, or a volcanic eruption;5. The layers of rock (or soil) in which fossils are found can tell scientists some of the geologic history of the geographical area in which the fossil was found. For example, sometimes seashell fossils are found in the rock of high mountains! That can only mean that the high mountain was once on the floor of an ocean or river. Over time, plate movement, volcanic eruption, and earthquakes have moved the old ocean floor (or river bottom) 'way up to the top of a mountain!

That is pretty important stuff! To geologists, it is very exciting.

 
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