Yummy eras!!
I did an activity that lasted the whole day!!! We made the layers of the different eras ( cezenoic, palentonic --- these are horribly misspelled I know) I think we discussed 3 or 4 eras. Then I had, chocolate pudding, cool whip and crushed oreos. (guess it was 3 eras)
I had gummy worms and Swedish fish which represented 2 diferent dinosaurs from different eras.
I had a big clear plastic container that we put the choc. pudding in and then put the gummy worms which we had to imagine were t-rex or whatever from that era. Then, after a PE or art or whatever, I pulled it out of the fridge and told the class they looked great for being millions of years old and we put the cool whip in with the Swedish fish and they were another kind of dinosaur from that period. We discussed which was the older layer etc, and would we ever find the gummy worm dinosaur in the cool whip era etc.....
Then after millions of years (or recess, lunch etc) they each got an oreo cookie which they smashed in a baggie and put it on the top which represented the era we are currently in with the rocks etc. on the top. Then........ the grand finale - they ate it!!
I had a paper that went along with it and they filled in the blanks and drew a picture. It was a big hit.
You might want to consider doing separate small glasses where they all make their own individual eras in a cup. They could just plop an era in as you go around with the pudding and cool whip. HAve fun whatever you choose.