Figure 1.4 Photosynthetic Organisms Changed Earth’s Atmosphere (A) Cyanobacteria are aquatic and photosynthetic: they live in the water and can manufacture their own food. Although they are quite small, they often grow in colonies large enough to see. (B) Colonies of photosynthetic cyanobacteria and other microorganisms produced structures called stromatolites that were preserved in the ancient fossil record. This section of fossilized stromatolite reveals layers representing centuries of growth. (C) Living stromatolites can still be found in appropriate environments.