A General Introduction First stages of evolution The earliest forms of life appeared about 3.7 x 109 years ago. Development of life on earth (biogenesis) was first a chemical, abiotic evolution, taking place in the oceans in the presence of phosphates (XPO4), silicates (XSiO4), metal ions, an atmosphere of nitrogen (N2), ammonia (NH3), carbon dioxide (CO2), methane (CH4), sulfur hydrogen (H2S), hydrogen (H2) and energy sources of heat, radiation and electric discharges. Formed were mixtures of amino acids, proteinoid microspheres with first forms of a membrane, metabolism, growth by budding. Biological evolution with nucleic acid chains capable of reproduction progressed in self-organization of matter with the basic forces of evolutionary drive of mutation, recombination, divergent development of structures and forms with specialization of functions, selection. Formed were protobiontes, containing a short DNA strand, which differentiated stepwise an improved metabolism, protein production, a multifunctional membrane. The first prokaryotes of blue algae and bacteria appeared. Following in the first evolutionary line were eukaryotes with differentiated organelles within the cell and a membrane enclosed nucleus, containing a chromosome set to control cell division by mitosis (start of phylogenesis). Their oldest known chalky fossils found in oceanic sediments are about 1.5 x 109 years old. The spreading one cell organisms took up mainly carbon and hydrogen containing molecules in exchange for nitrogen and oxygen to radically change the composition of the atmosphere, starting 2 x 109 years back, into the one we know today. During the Upper Precambrium of about 9 x 108 years ago the evolutionary rate of the diverse aquatic one cell organisms accelerated, forming multi cellular eukaryotes with specialized cell functions. The branches of plants and animals separated about 1 x 108 years back, introduced was sexual reproduction, further accelerating the evolutionary rate, and set up was a heterotrophic food chain with plants at the base, before the first forms of plant life appeared on land. |
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