Stromatolites and the cyanobacteria that make them are the earliest known life on Earth. Their evolution can be traced back some 3.8 billion years, and they are responsible for much of the oxygen that has made our atmosphere.
We have an assortment of stromatolites from various locations all over the world. They range in age, color, and form. As we search other worlds, stromatolites will certainly be on the radar for hopeful candidates of early life forms.