Stromatolites are layered mounds of single celled photosynthesizing microbes and were the only form of life on earth for the first 2 billion years. Easily recognizable by their laminated geological structure, these fossils should not be confused with Stromatoporoids (fossilized sponges). The easy way to tell the difference between the two is to look at the laminations. Stromatoporoids have small divisions representing the individual sponge cells and tend to look like graph paper, while Stromatolites have no vertical divisions, only horizontal laminations. See if you can see the laminations on the model above!
This object is scanned by Redpath Museum, McGill University