Final answer:
Fossilized remains of prokaryotes, especially microbial mats and stromatolites found in ancient rocks, are the best evidence for the evolution of prokaryotes around 3 billion years ago, supported by genetic evidence and molecular clock analysis.
Step-by-step explanation:
The best evidence that prokaryotes evolved about 3 billion years ago is a) Fossilized remains of prokaryotes. These fossilized remains include microbial mats, which are large multi-layered sheets of prokaryotes that date back about 3.5 billion years. These fossils are found in rocks and look like tiny bubbles or mats, which are recognizable as evidence of early life on Earth due to their relatively complex structure and large cell size for prokaryotes. Stromatolites are also critical fossils that suggest that prokaryotes lived in interactive communities. Furthermore, genetics and the principle of the molecular clock support the divergence and evolution of prokaryotes over billions of years because species that diverged long ago have genes that are more dissimilar.