The Griffith's experiment, the Avery-MacLeod-McCarty experiment, and the Hershey–Chase experiments were the set of experiments that established DNA as the key hereditary molecule. The Avery-MacLeod-McCarty experiment was an extension to the Griffith's experiment. The heat killed virulent S strain cells of the Griffith's experiment were lysed to form a supernatant containing a mix of RNA, DNA, proteins and lipids from the cell. The supernatent was equally divided into 3 parts after the removal of the lipids. The 3 parts were respectively treated with an RNAase to degrade the RNA, DNAase to degrade the DNA and proteinase to degrade the proteins. The treated supernatant was then added into the culture containing the non-virulent R cells. In case of the supernatant treated with the DNAse, no transformation of R cells into S cells occurred. The transformation of R cells to S cells occurred in the proteinase and the RNAse cases. This indicated that DNA was the hereditary molecule and not protein or RNA.

Cyanobacteria or simply known as blue-green algae may have formed the oxygen into the early atmosphere. This is because these micro-organism has the capability to photosynthesize wherein they can produce oxygen and carbohydrates. In fact, all the plants contribute in the fomation of oxygen.
Answer:
Energy can not be created or destoryed but converted.