How did bacteria changed Earth's atmosphere?

Early Earth probably had an atmosphere dominated by carbon dioxide similar to the atmosphere of Venus today.
# There are a group of one-celled organisms that can live in an oxygen free environment. These are the bacteria or prokaryotes. They do not have a nucleus and reproduce only by cell division. These creatures are the earliest evidence of life on earth. They were the first organisms to develop photosynthesis. Photosynthesis today is balanced by oxygen using respiration.

1. Hypothesis: Oxygen was nearly absent in the atmosphere of early Earth so photosynthesis would have created a net gain of oxygen first in the ocean and later in the atmosphere. Eventually with sufficient oxygen in the atmosphere respiration would have balanced photosynthesis except when burial removed the organic material from the oxygenated water or air. Before oxygen could build up in the atmosphere it must have oxidized reduced ions in seawater.
The most ancient bacteria forms (archaeobacteria) can use the chemical energy in hydrogen sulfide or other inorganic molecules to provide that energy (chemosynthetic). Fossil evidence shows that cyanobacteria
have existed on Earth for about 3 billion years. Cyanobacteria were able to use the electromagnetic energy of light to manufacture organic molecules through the process known as photosynthesis. The organic molecules contained chemical energy the cyanobacteria could use. The oxygen gas that was produced is poisonous to many of the anaerobic bacteria.