it's probably a little bit difficult to see, but there are some wavy and bulbous laminations, and those are features called stromatolites. narrator: stromatolites are rock-like structures usually formed by the trapping, binding, and cementation of sedimentary grains by microorganisms. dating back 3.5 billion years, they constitute our earliest and most pervasive record of life on earth. i think if you only had this rock to work with, you might be hesitant to even discuss whether it was evidence of life. but we can go to a number of places today, places like the bahamas, western australia, where stromatolitic structures are forming that connect this very ancient rock with the present day, where we can actually observe the processes that lead to this kind of pattern. narrator: it's believed that many ancient stromatolites were created by cyanobacteria, photosynthetic microorganisms that produce oxygen, implying that the cellular machinery for photosynthesis arose early in the planet's history. knoll: this tells us that life was present early in our planet's history, but let me show you an