Chapter 15 - Origin and Major Stages of Life Evolution on Earth

Abstract

This chapter discusses the main stages in the emergence and evolution of life on Earth and geologo-climatic processes, which led to the appearance on Earth of conditions conducive to the existence of higher life forms. The most important factor of life on Earth is the environment of the habitation of live organisms in the oceans and on continents. And the habitation environment is determined first of all by the Earth's climate—that is, by the composition, state, and temperature of the atmosphere whose origin and evolution was associated with the planet's degassing and with life activity of the organisms. The Earth's degassing begun at the Archaean/Katarchaean time boundary that resulted in the formation during Archaean of a relatively high-density, substantially reducing carbon dioxide–nitrogen–methane atmosphere. In Archaean also appeared volcanoes, differentiated magmatic rocks, and first isolated marine basins, which joined by the end Archaean into a single albeit shallow-water ocean. Due to a high atmospheric pressure, 5–6 atm., average oceanic water temperature, same as the troposphere temperature at sea level, rose in Archaean from +60 to +70 °С. As the atmosphere has carbon dioxide composition, the oceanic water has acidic reaction with pH ≈ 5.5–6.