Get the answer of: How Microbes Evolved on Earth?
The Earth, which began to form 4.6 billion (4600 Ma = megaanum, or million years) ago, had a reduced atmosphere before life originated on it. It is thought that the reduced atmosphere of earth consisted largely of gaseous forms of nitrogen, hydrogen, carbon dioxide and water vapour; with smaller amounts of ammonia, carbon monoxide and hydrogen sulphide.
Oxygen was either absent or present only in trace amounts and, therefore, the atmosphere was anaerobic (oxygen-free). Torrential rains poured over the developing Earth for centuries forming large masses of water in which the original gaseous raw materials of atmosphere gradually dissolved forming “oceans”.
The oceans were like a ‘broth’ and, with the aid of energy from ultraviolet rays and electrical discharges (lightening), variety of organic compounds were synthesized progressively in them by abiotic (non-living) reactions and these organic compounds slowly evolved into larger and more complex organic molecules (macromolecules).
Modern experiments have shown these reactions to be feasible. Also, under realistic conditions not involving enzymes, amino acids polymerize into polypeptides and nucleotides polymerize into nuclei acids.
However, the macromolecules had inherent tendency to aggregate in various combinations and appeared as distinct bodies (the microspheres) in the surrounding water medium. These microspheres are postulated to be the first step toward cellular organization and referred to as progenotes or Protobionts.
The protobionts possessed RNA as genetic material which was capable of directing the synthesis of more copies of RNA molecules, and then both genes and enzymes could have been made of RNA, perhaps between 4.0 to 3.5 billion years ago. In this ‘RNA world’, RNA served double duty of genes and enzymes.
The protobionts had evolved into bacteria-like cells by 3.5 billion years ago. Fossil cells that resemble bacteria were very abundant by then. The split between archaea and bacteria took place between 3.5 and 1.9 billion years ago, and the eukarya-archaea separated probably between 1.9 and 1.5 billion years ago.