Jello Fossil activity, Petrification, and Permineralization

As I prepared to teach about Sedimentary Rocks and Fossils, I was trying and trying to think of an activity that would teach about permineralization---the process during which minerals seep into the pores of dinosaur bones (or other materials) and harden, creating a hard, rock-like fossil. (As I understand it, Petrified wood and other petrified objects were first permineralized, and then some of the original material was actually replaced with minerals, until minerals are all that is left. Or, here is an even better explanation of permineralization versus petrification.)

(Also, here is a video about the petrified forest National Park that is quite interesting)

Anyway, the point is that I found lots of ideas for activities where you press a toy dinosaur into playdough and then call the impression a fossil, or put a leaf in plaster and paint it to look like stone, but none of them seemed very good at demonstrating the actual process of fossilization.

I was lying awake after Marigold's 3 a.m. feeding when it came to me like a flash of lightning. Jello! And ice! It was a brilliant idea. I will describe it.

So, I immediately got out of bed and went to the kitchen and filled several straws with water. I stuck them upright in a lump of clay, drizzled in some water, and then set them in an old spice jar and put them in the freezer.

In the morning, the straws were filled with long tubes of ice, as you can see.

Then I had Sam draw me a cute little dinosaur head, and I made a dinosaur. Here he is going on his merry Jurassic way.

The straws are his "bones."

The ice inside is the "organic material," like the bone marrow, etc.

I showed the children that the "bones" were solid, not hollow inside. They are just like the bones of an animal or dinosaur right after it dies.

Poor dinosaur! He was killed. His bones came apart. He fell into a lake bed.

Then he was covered by this "lake" of liquid jello. (I used this recipe for jello jigglers.) I told the children that the liquid jello represented mineral-rich water. The dinosaur bones sank to the bottom of the jello lake. (Actually, the bones were not heavy enough, so we had to put these knives on them to weigh them down. They have to be completely immersed in the jello solution.)

Next we put the jello in the refrigerator to set. This represented the long process of the mineral-rich water being compacted together with sediment, and forming into sedimentary rock.

When the jello was set, we pulled it out of the fridge and began to carefully excavate in the sedimentary rock.

We discovered our dinosaur's bones, and extracted them from the rock. We examined them. Were they filled with bone marrow (ice) anymore? They were not! The organic material had been replaced with another material---with minerals (jello), in fact! Instead of our dinosaur bones, we now had these permineralized fossil bones! (We squeezed them out of the straws to ascertain that they were, in fact, made of a wholly different substance than they had been made of at the beginning. The ice had melted and been replaced with jello!)

The jello actually proved to be a very good medium for demonstrating other fossil types as well. There were these knives, preserved intact in the substance, much like insects preserved in amber.

And there were these impressions left by the "bones," perfect molds, much like dinosaur footprints or other impression fossils.

If I were doing this activity again, I would put even more objects in the jello. It was really fun for the children to "dig" for these fossils and separate them from the "rock," and it was quite an effective way to teach the concepts of casts and molds as well. But I think the permineralization object lesson was the best part---it worked just as I wanted it to and it was a memorable way for us to remember that concept!