Date Event 2500 Ma Great Oxygenation Event led by cyanobacteria 's oxygenic photosynthesis. Commencement of plate tectonics with old marine crust dense enough to subduct. 2000 Ma Diversification and expansion of acritarchs. By 1850 Ma Eukaryotic cells appear. Eukaryotes contain membrane - bound organelles with diverse functions, probably derived from prokaryotes engulfing each other via phagocytosis. (See Symbiogenesis and Endosymbiont). Bacterial viruses (bacteriophage) emerge before, or soon after, the divergence of the prokaryotic and eukaryotic lineages. The appearance of red beds show that an oxidising atmosphere had been produced. Incentives now favoured the spread of eukaryotic life. 1400 Ma Great increase in stromatolite diversity. By 1200 Ma Meiosis and sexual reproduction are present in single - celled eukaryotes, and possibly in the common ancestor of all eukaryotes. Sex may even have arisen earlier in the RNA world. Sexual reproduction first appears in the fossil records; it may have increased the rate of evolution. 800 Ma First multicellular organism may have arisen. 750 Ma First protozoa (ex: Melanocyrillium) 850 -- 630 Ma A global glaciation may have occurred. Opinion is divided on whether it increased or decreased biodiversity or the rate of evolution. 600 Ma The accumulation of atmospheric oxygen allows the formation of an ozone layer. Prior to this, land - based life would probably have required other chemicals to attenuate ultraviolet radiation enough to permit colonisation of the land. 580 -- 542 Ma The Ediacara biota represent the first large, complex multicellular organisms -- although their affinities remain a subject of debate. 580 -- 500 Ma Most modern phyla of animals begin to appear in the fossil record during the Cambrian explosion. 560 Ma Earliest fungi 550 Ma First fossil evidence for Ctenophora (comb jellies), Porifera (sponges), Anthozoa (corals and sea anemones)
when did the first protozoa appear on earth
750 Ma