Abstract:

Increasing evidence suggests that life most likely originated in a time between ca 3.9 and 3.6 Ga on the earth, with the earliest recognizable fossils recorded in the rocks of ca 3.5 Ga. Besides carbon, water, nitrogen, hydrogen, and phosphorous are indispensable chemical elements, while clay minerals and metal sulfides are key catalysts for organic synthesis. Early environments with saline water and hydrothermal activity seem to be the most favorable hatch pool for the origin of life. Since prokaryotic organisms emerged not later than ~3.5 Ga, biosphere as an important geologic agent interacting with atmosphereocean has greatly accelerated the evolution of Earth surface systems, showing an apparent coevolution with environments. As one of the most important events in Earth history, the Great Oxygenation Event (GOE) has not only altered the earth surface environments profoundly, accelerated various geologic processes and the generation of new minerals, but also reset the ocean chemistry and element cycles. GOE resulted virtually from the onset of oxygenproducing photosynthesis, and the overall transition of ocean chemistry at ca 1.8 Ga was also closely related to microbial processes. The emergence of metazoans at the terminal Neoproterozoic and their rapid diversification at the beginning of the Phanerozoic are significant innovations in life evolution. These innovations are closely linked to the further increase of atmospheric oxygenation and the consequent changes in ocean chemistry at the times, particularly to the shrinkage of euxinic waters and the increasing availability of bioessential elements in seawater, in which microbes always play essential roles.

Key words: origin of life, early biotic evolution, atmospheric oxygenation, ocean redox changes, life-environment interactions.