Abstract:Early traceability and evolutionary trend research of eukaryotes became an international hot spot for the research necessary of habitable earth, exploration of extraterrestrial life and resource exploration. Based on the evidence of body fossils, molecular fossils and molecular clocks that have been reported, the evolution of Proterozoic eukaryotic algae is divided into four stages: environmental preparation (2.45~1.70Ga), slow development (1.70~0.80Ga), rapid rise (0.80~0.64Ga), and radiation (0.64~0.54Ga). The emergence and radiation process of Proterozoic eukaryotes were coupled with the oxidation events and extreme geo-climatic events (such as glaciation events), showing co-evolution of early life and the earth surface environment. The slow development of eukaryotic algae during 1.70~0.80 Ga might be related to the long-term low atmospheric oxygen content (approximately equal to 1~10% PAL of the present level). The low degree of atmospheric-oceanic oxidation not only limits the living space of eukaryotic algae, but also restricts their primary productivity through constraining the supply of nitrogen and phosphorus. Therefore, surface environment oxidation may be the key factor for the habitable evolution of the earth and the appearance of various complex life, especially the eukaryotes. Exploring the biosphere evolution from the perspective of the formation and evolution of the earth system may give more reliable answers to the past and future of life.
