The answer is B. This is stipulated in the theory of abiogenesis. The atmosphere in early earth was composed of compounds such as methane, hydrogen sulfide, and ammonia. This reducing environment was right for the formation of biomolecules . This early life is similar to that found in hydrothermal vents deep in the oceans, today.
Answer: d) increasing colonies of cyanobacteria undergoing photosynthesis.
Explanation:
Cynobacteria were the microorganisms which used to live around 3.5 billion years ago primarily in the seawater. They are believed to be the first photosynthesizing organisms on primitive earth. They were capable of using light energy from sun, to produce organic carbon the building blocks of life and released oxygen gas in the seawater. The oxygen enters the seawater and then liberated into the atmosphere. The dead cynobacteria buried into the seafloor sediments. The decomposition of the cynobacteria has resulted in the liberation of the oxygen again in the seawater. This can be supported by the carbon burial theory which suggests the fact that when the organic material is buried after decomposition it liberates the oxygen into the atmosphere. With the evolution of these photosynthesizing bacteria into complex life forms has increased the amount of organic carbon available as the biomass. The decomposition of this biomass has increased the abundance of oxygen into the atmosphere.
