the first bacteria appeared on earth about 4 billion years ago.
the first bacteria appeared on earth about 4 billion years ago.
when did the first bacteria appear on earth?
about 4 billion years ago
the ancestors of modern bacteria were unicellular microorganisms that were the first forms of life to appear on earth, about 4 billion years ago. for about 3 billion years, most organisms were microscopic, and bacteria and archaea were the dominant forms of life. although bacterial fossils exist, such as stromatolites, their lack of distinctive morphology prevents them from being used to examine the history of bacterial evolution, or to date the time of origin of a particular bacterial species. however, gene sequences can be used to reconstruct the bacterial phylogeny, and these studies indicate that bacteria diverged first from the archaeal/eukaryotic lineage. the most recent common ancestor of bacteria and archaea was probably a hyperthermophile that lived about 2.5 billion–3.2 billion years ago.
bacteria
purple bacteria were the first bacteria discovered to photosynthesize without having an oxygen byproduct. instead, their byproduct is sulfur. this was demonstrated by first establishing the bacteria's reactions to different concentrations of oxygen. what was found was that the bacteria moved quickly away from even the slightest trace of oxygen. then a dish of the bacteria was taken, and a light was focused on one part of the dish leaving the rest dark. as the bacteria cannot survive without light, all the bacteria moved into the circle of light, becoming very crowded. if the bacteria's byproduct was oxygen, the distances between individuals would become larger and larger as more oxygen was produced. but because of the bacteria's behavior in the focused light, it was concluded that the bacteria's photosynthetic byproduct could not be oxygen.
purple bacteria