This is taken from a lesson in the Investigating the Possibilities series by Master Books that will be on the market soon. It is in the Water and Weather book by Tom DeRosa and Carolyn Reeves.
A fun activity to teach students more about how footprints, casts, and molds formed during the Great Flood.
Make a “fossilized” footprint.
Smooth out about ½ to ¾ cup of playdough in a large paper plate. Use a roller or PVC pipe to roll over the clay until it covers the bottom of the plate. Now turn the clay over so the smooth side is up.
Recruit a volunteer with a fairly small foot. Rub the student’s foot with petroleum jelly. The student should carefully press his foot into the clay as if walking, and then clean the petroleum jelly and clay off his foot.
Take some more clay (about ½ to ¾ cup) and roll it into a tube or “snake” that is about an inch in diameter and long enough to go around the clay in the paper plate. Place the tube around the edge of the clay and press it into the bottom piece of clay to make a seal. Squeeze and flatten the tube to make a wall around the footprint impression to make a bowl that can hold the liquid plaster.
Now measure out 2 cups of Plaster of Paris into a disposable container. Measure 1 cup of water, and pour it slowly into the plaster, stirring and mixing continually. If the mixture is still dry, add more water a little at a time until it is like pudding. When mixed well, pour about half the plaster over the impression in the clay. Lift your plate with two hands a few cm high and let it plop down on the table. Do this a few more times. This will spread the plaster and bring air bubbles up to the surface.
Allow the plaster to harden. It should harden in an hour or more. After it has hardened, carefully remove the plaster from the clay and observe the impression of the footprint. Look at the clay as well as the plaster.
1. Describe the impression in the clay.
2. Describe how the bottom of the Plaster of Paris looks.
Make a leaf mold.
While your plaster is still wet, put some of it in a small meat tray. Rub the leaf with petroleum jelly. Quickly, but gently, place a leaf on top of the plaster and cover with plastic wrap. Use a block to gently press the leaf into the plaster. (Do not push down to bottom of the tray.) After it has thoroughly hardened, remove the leaf. Compare the leaf to the leaf mold.
The Science Stuff
Not all fossils are remains of once-living plants and animals. Trace fossils are fossils where nothing is left except a footprint or an impression of where the organisms had been. The impression of the footprint in the clay represents this kind of fossil.
Some fossils have been made by something like a stem with flowers, or leaves, or maybe a shell that left their impression in wet sediment. If something is pressed into wet sediment and becomes a fossil, the impression left behind is called a mold. If part of the actual organism gets trapped in the sediment or a new layer of sediment fills in the mold and hardens, that is known as the cast.
The vast majority of fossils are organisms without a backbone that once lived in an ocean. These include trilobites, crinoids, ammonites, and corals. Within this group, the most commonly found fossils are casts and molds of animals with hard shells, such as clams and brachiopods.
You might think that a few footprints wouldn’t leave much information, but it actually tells paleontologists a lot more than you would think--things like the kind of animal that made the print, how heavy it was, if it was limping, or if it was running or walking.
The animal’s weight can be estimated by comparing the depth of the footprint made with other footprints. The more the animal weighs the deeper the print. A lighter-weight animal will make a more shallow print. The distance between footprints is another important clue as to how large the animal was. Large animals take bigger steps than smaller animals.
Paleontologists can often make a positive identification of an animal based just on the footprint. Sometimes a footprint cannot be positively identified, but can still be put into a category of the type of animal. Dinosaurs, for example, might be classified as theropods (certain dinosaurs that stand on 2 feet) or sauropods (large dinosaurs that stand on 4 feet).
Footprints are only preserved under special conditions that occur before the prints can be eroded or washed away. Because these conditions must occur quickly after the prints have been made, it’s surprising that actually billions of footprints have been preserved in rocks.
Fossil footprints have been found in a number of places throughout the world. One
of the most famous sets of tracks is known as the Laetoli footprints, which were
made in volcanic ash that hardened into rock. These tracks include footprints from
a variety of animals, as well as footprints that appear to be human-like. Some
scientists doubt that humans made any of the footprints because radiometric dating
of surrounding rocks indicated the prints were about 3 ½ million years old. An artist
drew a picture of all the animals that left footprints. A number of animals were
identified from their tracks. However, for the footprints that looked human, the
drawing included an ape-like animal that walked upright. These footprints resemble
the barefoot Indians that exist today in the rugged mountains of Peru. We know that
radiometric dating of volcanic rocks is not always correct, so there is no reason to
doubt that these human-like footprints were produced from a real human rather than
an ape-like animal.
A prominent light-colored layer seen in the Grand Canyon, known as the Coconino
sandstone, contains numerous distinct fossil footprints of small amphibians or
reptiles. Scientists disagree on whether these footprints were formed in desert sand
or in sand that was under water. The authors believe that all the upper layers of the
Grand Canyon were laid down rapidly as a result of a catastrophic worldwide flood.
It’s hard for us to imagine how there could be a desert in the middle of a worldwide
flood. One researcher found that certain kinds of salamanders could swim under
water, but often preferred to walk across the bottom of a tank of water in sand.
These salamanders left distinct footprints under water and in wet sand, but not in
dry or damp sand. This research supports the idea that the sand formations could
have been produced underwater rather than in desert conditions.
This is a part of a lesson about on how fossil footprints and other molds and casts can form. These kinds of fossils are very common, but they only form in rocks under rare conditions. The conditions that were present during and after the Genesis Flood would have been just right for forming fossils. Unless the prints were quickly covered up by new layers of sediment, they would have been washed away or eroded. The Flood would have provided many other ideal conditions for forming fossils.