What are the oldest bacteria?

The oldest are cyanobacteria. They were among the first to appear on our planet. These organisms are prokaryotes, that is, they do not have complex membrane organelles in their structure. But despite this, cyanobacteria have an autotrophic type of nutrition. They are capable of photosynthesis, and also provide our planet with 90% oxygen. But not all cyanobacteria release oxygen during photosynthesis. The dating of the oldest fossils of these bacteria is 3.7 billion years, which confirms the origin of life at that time.