An early filamentous prokaryote (Campbell, 1992)
Stromatolites are formed by unicellular organisms called Cyanobacteria (formally known as blue-green algae).. Cyanobacteria are Prokaryotes, which are known to be the earliest forms of life, throughout time they have adapted to the changing earth, and in turn help it evolve. Prokaryotes belong to the kingdom Monera (Greek for single) and are small celled organisms that lack membrane-enclosed organelles. They have cell walls, but their composition differs from those of plants, protisits and fungi. They are similar to Eukaryotes, but they have smaller and simpler genomes, and differ in genetic replication, protein synthesis, and recombination. Prokaryotes are photosynthetic and aquatic and can exist in almost any environment, and individually their impact may be microscopic, but collectively their impact on the earth is immense. Prokaryotes are divided based on the differences on how they receive their nutrition (how they obtain energy and carbon). Cyanobacteria belong to the category termed photoautorophs, which use light to drive the synthesis of organic compounds from carbon dioxide.
c) vertical section through layered, unlithified microbial mat; d) Coccoid cyanobacteria
from marine microbial mat; e) Filamentous cyanobacteria (Awramik, 1972)