Cyanobacteria, also known as blue-green algae, are photosynthetic bacteria that produce oxygen as a byproduct of their metabolism. They play a crucial role in the formation of stromatolites. Here's how:

* Photosynthesis: Cyanobacteria use sunlight to convert carbon dioxide and water into sugars and oxygen.

* Sediment Trapping: As cyanobacteria grow and reproduce, they form mats on the surface of water bodies. They trap sediment (sand, mud, etc.) with their sticky layers, forming layers within the mat.

* Calcium Carbonate Precipitation: Some cyanobacteria also precipitate calcium carbonate, contributing to the hardening of the mat.

Over time, these layers accumulate, creating the layered structures we recognize as stromatolites.

Stromatolites provide important evidence of early life on Earth and are a testament to the power of cyanobacteria in shaping our planet's atmosphere and environment.