Evolution, Chemical

Chemical evolution is the process of the synthesis of biochemically important molecules starting from simple molecular building blocks, such as water (H20), nitrogen (N2), carbon dioxide (C02), and hydrogen sulfide (H2S), under plausible primordial conditions that governed the prebiotic Earth. It describes a process of increasing complexity from simple inorganic compounds toward first simple organic compounds that in turn formed biochemically important structures for a first living system. First life may have started up as a final product of chemical evolution. This event is probably the result of a multitude of processes, most of them not very likely, that led to a proper arrangement and activation of complex molecular building blocks.

Chemical evolution on a timescale is preceded by the formation of elements in stars in consecutive nucleosynthetic processes and by the formation of [Page 456]first simple compounds in space at a later stage. Eventually, interstellar matter aggregated to form the solar system and the terrestrial planets, Earth, Mercury, Venus, and Mars, about 4.6 billion years ago.

Chemical evolution on Earth is a process that probably started later than about 3.8 billion years ago. It is difficult to date the single stages even roughly, as little geological and chemical record remains. During the following millions of years chemical evolution must have led to the origin of life on Earth, as the oldest-known fossil records stem from a period about 3.5 billion years ago.

Chemical evolution is a development that is strongly influenced by the environment of the terrestrial planet, such as composition of the atmosphere, types of radiation, and geology. Any development is determined by the laws of nature and statistics. Therefore, it should be possible to simulate basic chemical processes that occurred several billion years ago. A fundamental problem, however, is the lack of knowledge about the exact environment on planet Earth at that time. Because of the lack of knowledge, the possibility to plausibly reconstruct the process of chemical evolution is very limited.

Not only does the environment affect chemical evolution, but chemical evolution changes the environment. Molecules are formed and altered. There will be a kind of competition between molecules for nutrients. The rate of formation as well the rate of destruction is decisive for an enrichment of certain types of molecules.

Chemical evolutionary processes, in general, should not be limited to Earth but could also proceed on any terrestrial planet because principal chemical laws should be valid throughout the whole universe.