These lovely specimen jars look really complicated but couldn't be easier, especially if you have a few spare dinosaurs roaming around the house. If you don't have any extras, please drop me an email and I'll send you any of the four-freaking-dozen that I pick up on an hourly basis.
Anyhoo. Take a big jar, fill with pebbles, then dirt. Add plants and dinos. Bingo. Project done.
If you need more thorough instructions, this tutorial from two straight lines will give you everything you need, including a source for the big jars.
I'm also envisioning a few of these filled with the forty-gazillion small plastic sea creatures we have and/or the ninety-gabillion space aliens. Everyone likes plants, don't they? Even aliens?
Photo credit: Courtney