The Origins of Life

The Origins of Life, described hypothetical conditions which he felt would have been necessary for life to first come into existence on early Earth.
He thought the atmosphere was made largely of water vapor (H2O), carbon dioxide (CO2), carbon monoxide (CO), nitrogen (N2), methane (CH4), and ammonia (NH3). As the surface of Earth cooled again, torrential rains of this mixture formed the first seas, the “primordial soup.”

Lightening, ultraviolet (UV) radiation, and volcanic action all were more intense than they are now.


  1. First, organic monomers (simple sugars, amino acids, fatty acids, and nucleotides) would have to be synthesized abiotically from inorganic substances like methane, carbon dioxide, and ammonia. This hypothesis was later tested by an experiment done by Stanley Miller as a grad student under Harold Urey in 1953. H2O, H2, CH4 and NH3 (at that time, thought to be components of the early atmosphere) were placed in a sterile, closed system. Heat was added to mimic the heat from volcanic activity, and electric sparks were provided to mimic lightening. After one week, the contents of this system had turned from clear to a murky, brown color. A chemical analysis showed a number of organic compounds were present, including several amino acids and simple sugars. Other researchers have since tried similar experiments with slight variations in the initial mix of chemicals added, and by now, all 20 amino acids, and a number of sugars, lipids, and nucleotides have been obtained in this manner. From this experiment, scientists generalize that if this can happen in a lab, it could have happened in a similar way on early Earth.
  2. The second step would be the formation of organic polymers and genetic material from the existing monomers (polysaccharides from simple sugars, proteins from amino acids, and RNA from nucleotides), possibly using hot sand or finely divided clay as a catalyst.
  3. Thirdly, it is thought that non-living aggregates of these polymers formed. These may have exhibited some properties characteristic of living organisms, but were NOT ALIVE, and did not have all the properties of living organisms. In a research laboratory, scientists have seen mixtures of proteins, lipids, and carbohydrates form globules. If the proteins involved happen to be enzymes, these globules can even carry on "metabolic" activity, although they have no means to replicate themselves. Simultaneous to this, the genetic code would have to have arisen. Several widely-accepted theories as to how this may have happened include the possibly involvement of damp, zinc-containing clay as a catalyst to help the nucleotides polymerize first into RNA, and later into DNA.
  4. It is thought, then, that about 4.1 to 3.5 bya, the first prokaryotes, like bacteria, came into existance. It is difficult to pinpoint a date for this because bacteria don't have skeletons to leave behind. The first “fossils” (remains of colonies/secretions) of prokaryotes seem to be this age. These would have been very simple cells without many of the organelles present in modern cells, especially modern eukaryotes. Once the first cells, the first living organisms, the first prokaryotes came into existance, then the Theory of Evolution takes over to provide an explanation for how (not why) these primitive cells diversified into the five kingdoms of life which we recognize today. Initially, the energy needed for growth and development was supplied by glycolysis and fermentation. There was no free oxygen in the early atmosphere, and indeed, any organisms living back then would have probably been poisoned/killed by this highly-reactive chemical. Only later, as photosynthetic organisms released increasing amounts of this toxic waste into the atmosphere, did the process of cellular respiration evolve as a means of making use of this oxygen.

Initially, the energy needed for growth and development was supplied by glycolysis and fermentation. There was no free oxygen in the early atmosphere, and indeed, any organisms living back then would have probably been poisoned/killed by this highly-reactive chemical. Only later, as photosynthetic organisms released increasing amounts of this toxic waste into the atmosphere, did the process of cellular respiration evolve as a means of making use of this oxygen.