Final answer:
Cyanobacteria are ancient photosynthetic bacteria that produced oxygen over 2.5 billion years ago, contributing significantly to the oxygenation of the Earth's atmosphere and influencing the direction of evolution.
Step-by-step explanation:
Early Photosynthetic Bacteria: Cyanobacteria
Early photosynthetic bacteria, known as cyanobacteria, played a crucial role in shaping our planet's atmosphere. These ancient organisms contain photosynthetic pigments and were responsible for the production of oxygen more than 2.5 billion years ago. Cyanobacteria, once referred to as blue-green algae, possess chlorophyll and carry out oxygenic photosynthesis. The fossil evidence of early photosynthesis can be observed in formations such as stromatolites. Divergence timelines indicate that bacteria and archaea split from common ancestors billions of years ago, with cyanobacteria contributing significantly to the oxygenation of Earth's atmosphere. This event radically changed the direction of evolution, enabling the rise of more complex life forms that depend on oxygen, and is closely linked to adaptations for surviving on land.