Origin of Life

How old is the earth?

Radioisotope dating suggests a slightly older earth

The earth (and the other planets) condensed out of a swirling cloud of gas surrounding the primitive sun.

The atmosphere of the primitive earth was rich in hydrogen, both in the elemental state and united with carbon in methane, with nitrogen to form ammonia, and with oxygen as water vapor.

Atmospheric water vapor condensed into rain. Eroded surface. Washed minerals into seas. Chemicals from atmosphere mixed and reacted with those in the waters to form many hydrocarbons.

The view that life emerged through a long process of chemical evolution was set forth by the Russian biochemist Alexander Oparin in 1924.

Oparin pointed out that the transformation of lifeless chemicals into living matter extended over a period of almost a billion years. He also argued that such a transformation would not be possible today, since any particle approaching the form of life would be decomposed by the oxygen of the air or destroyed by microorganisms.

Hydrocarbons, water and ammonia are the raw materials for amino acids.

In the early days of chemistry, it was believed that organic compounds could only be produced by living organisms. But, in 1828, Friedrich Woller was able to manufacture the organic compound urea under laboratory conditions. Since then, many organic compounds have been artificially synthesized.

In 1953, Stanley Miller synthesized organic compounds under conditions resembling the primitive atmosphere of the earth. He passed electrical sparks through a mixture of hydrogen, water, ammonia and methane.

The electrical discharges duplicated the effects of violent electrical storms in the primitive atmosphere. In the laboratory, four simple inorganic molecules interacted, after just a week, for produce several kinds of amino acids.

A number of energy sources would have been available to provide the “spark of life”.

Others have suggested that deep-ocean geothermal vents provide a suitable location for the formation of organic chemicals.

…..or under the ice covering the primitive ocean.

However, synthesis of amino acids is just a first step. In 1964, Sidney Fox heated a mixture of 18 amino acids to temperatures of ºC. for varying periods of time. He obtained stable, proteinlike macromolecules which he termed proteinoids.

When the proteinoid material was cooled and examined under a microscope, Fox observed small, spherical units that had arisen from proteinoid aggregations. These microspheres showed a general resemblance to simple bacteria.

It is likely that self-replicating polynucleotides slowly became established some 3.5 billion years ago. Natural selection likely operated on these populations of molecules just as it does on organisms, and the molecules became more efficient in the storage and transfer of information.

Certain polynucleotides not only specified their own sequences, but directed the synthesis of polypeptides. In present-day organisms, RNA guides protein synthesis, which suggests that nucleotides of RNA were the first carriers of genetic information.

At some later stage, DNA took the place of RNA as the repository of genetic information. Thus, in modern cells, genetic information is stored in DNA, transcribed into RNA, and translated into protein.

The universality of the genetic code suggests that this became established a very early stage or organic evolution. Remember Kirk’s aliens.

A protein specified by a particularly efficient variant of RNA could not speed up the reproduction of that kind of RNA unless in were somehow restrained in the area of that RNA. If some form of compartment evolved to enclose the protein, it would prevent free diffusion. All present day cells have a plasma membrane composed of phospholipids. It is not implausible that the first cell was formed when polarized films of phospholipids formed “bubbles” enclosing aggregations of complex molecules.

The oldest known fossils are of cyanobacteria some 3.55 billion years old.

Primitive autotrophs would require a whole array of enzymes to direct a multistep chain of reactions involved in the synthesis of a protein. It is probably too much to expect that all of the necessary enzymes evolved at the same time. Norman Horowitz of the California Institute of Technology suggested that the chain of steps could have evolved backward.

What about the evolution of eukaryotes?

The “endosymbiont hypothesis” suggests that organelles like mitochondria originated as endosymbiotic bacteria living within the cell membranes of other organisms.

Many properties of modern eukaryotic cells and their organelles suggest that this is a possibility.