Final answer:
Stromatolite fossils from 3.5 billion years ago suggest life started earlier, around 3.9 billion years ago, with the presence of photosynthetic prokaryotes like cyanobacteria playing a key role in oxygenating the Earth's atmosphere.
Step-by-step explanation:
Stromatolite fossils that formed 3.5 billion years ago indicate that A. life must have arisen quite a bit earlier, perhaps 3.9 billion years ago.
Stromatolites provide evidence that by the time the oldest surviving rocks were formed, life already existed, and these organisms had evolved to be capable of forming large colonies.
One of the significant types of organisms that existed back then were photosynthetic prokaryotes, otherwise known as cyanobacteria, which played a crucial role in the evolution of oxygenic photosynthesis and the subsequent accumulation of oxygen in the Earth's atmosphere.
During the early periods of Earth's history, life was predominantly microbial, consisting of chemosynthetic and photosynthetic prokaryotes, with oxygen-producing cyanobacteria leading to major environmental transformations.