This week's experiment is a combination of ideas. The seed for this idea came from a homeschooling list member that wanted information on soil testing. They wanted to test and compare soils from different parts of the country. Connected to this was all of the information that we got on paleoecology while digging dinosaur bones. The sediment around a fossil can tell us quite a bit about the environment where it was deposited. To do this experiment, you will need:
- a large jar with a tight fitting lid
- water
- soil
- crayon or grease pencil
Fill the jar about 2/3 of the way with water. Then add enough soil to bring the water level up to about an inch from the top. Put the lid securely onto the jar and shake it vigorously for about a minute. You want to be sure that all of the particles in the soil are loosened and that there are no clumps left.
Once you have everything very well mixed, place the jar in a place where it can sit for 24 hours without being disturbed. Watch it carefully. After one minute, use the crayon to make a mark at the top of the sediment that has settled out. This is the sand part of your soil.
Let the jar continue to sit undisturbed for one hour. You will notice that more of the sediment has settled out. Mark the top of the new layer. This layer is made up of silt sized particles.
Again, let the jar stand without being moved or jostled. I know it is hard not to pick it up and look more closely at the layers. Have patience and wait. After 24 hours, most or all of the sediment should have settled out, leaving clear water above the sediment. This last layer is the clay part of your soil. It has the tiniest particles and takes the longest to find its way to the bottom. Make a mark at the top of the clay layer.
Now that you have separated your soil into sand, silt and clay, you can determine what kind of soil you have. At my house, this is a quick, easy experiment. Living at the beach, we have very sandy soil, with almost no silt or clay.
You may have loam soil, which has fairly even amounts of sand, silt and clay. This is the ideal kind of soil for your garden. It has plenty of nutrients and drains well.
If your soil has mostly clay, then you have (can you guess?) Clay soil.
In addition to seeing the make-up of your soil, this experiment can also give you an idea about the environment where different kinds of sediments are deposited. Some of the dinosaur bones that we were digging were found in layers of sand, while at another site, there were bones in a layer of clay. From our experiment, we can begin to think about what the areas were like when the bones were buried. The clay layer would seem to indicate still water, sitting in a swamp or marsh, while the ribbon-like layers of sand look to have been flowing streams.