I grew up in coal mining territory and one of our favorite childhood activities was going to church camp in the summer because in our free time we would hunt for fossils in the huge stacks of coal and rock scrap in the field beside the church. Yeah, probably not that safest place to be playing…
Anyhow, it wasn’t unusual to find fossil imprints in these rock piles, oftentimes they were of ferns though we found a few bug imprints too. We’d take our treasures home and proudly display them until our mothers removed them because the coal really did turn pretty much everything it touched black.
It takes a long time for a fossil imprint to be preserved but you can replicate the process at home. Fortunately the process described below only takes a few days versus tens of thousands of years.
P.S. In addition to being a fun hands-on science lesson this is a great sensory activity as well.
The kids and I use a dough that contains coffee for our fossils, we’ve been doing it this way for a lot of years. There are plenty of recipes for this dough on the internet but the mixture I list below is what ended up working best for us. The proportions of ingredients are a little different than what you commonly see online. If your dough ends up being too wet add some more flour, and if it’s too dry add a bit more cooled coffee.
And if you’re wondering…yes. Yes I did drink all the coffee necessary for this craft. It took me about 3 days to save up enough grounds from our single-serve machine to do this craft. (On a side note, thanks to all the extra caffeine my house is cleaner than it’s been in months, maybe even years.)
1 C coffee grounds (brewed & dried)
2/3 C coffee (brewed & cooled to room temperature)
1/2 cup salt*
1 cup (-ish) of flour
Pour all of the above into a large bowl. Mix well with your hands until it is a nice doughy consistency.
Break off a piece of dough that is about the size of your palm. Have the children roll it around to make a ball, then flatten int to about 1″. I highly suggest doing this step on waxed or parchment paper.
Press some kind of object into the dough. We used seashells since they’re readily available here, but you can also use leaves & twigs, a winged bug (preferably one that died of natural causes) or anything you think would make a cool imprint. My kids even tried their own fingerprints!
Remove the object and if you’re happy with the imprint let it dry completely, which can take up to 48 hours. If you want to try again just smoosh the dough into a ball and repeat the process.
This recipe will make 4 fossil imprints that are on the larger size but you can easily divide the dough up into smaller bits to make smaller imprints.
*I actually used 1/3 cup of salt for the dough that made the imprints you see here, and only because I ran out of salt. The salt will help to preserve the imprints, so if you want to keep them long term add more salt or spray them with a clear coat paint
What this replicates:
Have you ever picked up a rock and seen the pattern of a leaf in it? This is a fossil imprint! What happened is that a long, long time ago a plant fell onto a piece of rock or into a mud puddle. Much like when you press your finger into dough, a print is formed. Over time other things fell on top of the leaf print; perhaps it was dirt, more mud, rocks, etc. As the years pass the rock/mud hardens & the leaf rots away but the imprint is left behind.
Recommended age: all
Reading level required: none
Skill level required: none
Parental involvement: highly recommended