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 bacteria to appear on Earth, some 3.8 billion years ago, had no choice but to be anaerobic, because the atmosphere at that time contained no oxygen.

Detailed explanation-4: -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-5: -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.