AP BIOLOGY

Detailed explanation-1: -Prokaryotes were the earliest life forms, simple creatures that fed on carbon compounds that were accumulating in Earth’s early oceans. Slowly, other organisms evolved that used the Sun’s energy, along with compounds such as sulfides, to generate their own energy.

Detailed explanation-2: -Life arose in a world without oxygen and the first organisms were anaerobes.

Detailed explanation-3: -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.

Detailed explanation-4: -Bacteria are the only known inhabitants of earth for at least the first 1.5 billion years in the history of life. Genetic comparisons suggest that the oldest, most primitive bacterial lineages were anaerobic and the ability to survive in the presence of oxygen evolved separately in different lineages.

Detailed explanation-5: -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.