AP BIOLOGY

Detailed explanation-1: -Bacteria were the first organisms to appear on the earth. At that time the environment was devoid of oxygen. Hence, these first bacteria were anaerobic and they were also heterotrophic due to lack of photosynthetic activity. These bacteria used to feed on carbon compounds that were present in ocean water.

Detailed explanation-2: -The earliest life forms we know of were microscopic organisms (microbes) that left signals of their presence in rocks about 3.7 billion years old. The signals consisted of a type of carbon molecule that is produced by living things.

Detailed explanation-3: -The first life forms were anaerobic as the primitive atmosphere was reducing and oxygen was absent. They were chemoheterotrophs that used the organic component as a source of energy and carbon.

Detailed explanation-4: -Bacteria were the very first organisms to originate as life on the earth. As in the primitive earth, the oxygen was limited, there were only anaerobic heterotrophic bacteria.

Detailed explanation-5: -Life arose in a world without oxygen and the first organisms were anaerobes. Here we investigate the gene repertoire of the prokaryote common ancestor, estimating which genes it contained and to which lineages of modern prokaryotes it was most similar in terms of gene content.