This is something I have seen done in a number of ways. String stretched out is a great visual for younger students. Paper clipped pictures can be used to represent organisms at different stages. Phylogenetic trees can be built up in the same way by making the string branch. I have also used the old style computer paper (with continuous sheets) to cover time periods along the classroom wall. The more that students contribute to the project (calculating the appropriate length; measuring out to points where organisms should be added; sketching the organisms....) the more it will hold their attention.