The first bacteria that appeared on Earth are known as stromatolites or more specifically, Cyanobacteria. These ancient microorganisms were among the first forms of life, thriving in aquatic environments over 3.5 billion years ago. Stromatolites are layered structures created by the activities of cyanobacteria, which contributed significantly to the production of atmospheric oxygen through the process of photosynthesis. Their existence paved the way for more complex life forms and ecological diversity seen today.