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.

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.

Detailed explanation-3: -The first fossils of prokaryotic (bacterial) cells are known from 3.5 and 3.4 billion years ago. These bacteria were photosynthetic (although non-oxygen producing) so it is likely that simpler non-photosynthetic bacteria evolved prior to this (Schopf, 1987; Beukes, 2004).

Detailed explanation-4: -The first life form, bacteria like prokaryotic cell, originated from protocell in the Archaeozoic era (3800 million yrs ago, the era of the dawn of life). The first life forms were anaerobic as the primitive atmosphere was reducing and oxygen was absent.

Detailed explanation-5: -The earliest known life forms on Earth are believed to be fossilized microorganisms found in hydrothermal vent precipitates, considered to be about 3.42 billion years old.