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  4.5 BILLION YEARS AGO
 radiometric dating of meteorites deposit on earth
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  4.6-4.0 BILLION YEARS AGO
 period from earths formation to approximate time of emergence of life, moon formed, no life exists
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  4.0-2.5 BILLION YEARS AGO
 most rock was lava/magma based
 atomosphere lacked free oxygen
 unicellular life existed
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  3 BILLION YEARS AGO
 iron oxide in rocks could only fomr in presence of atmospheric oxygen, essential for cellular respieration
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  2500-542 MILLION YEARS AGO
 photosynthesis causes the oxygentation of earth, eukaryotes evolve,
 endosymbiosis emerges.
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  1.8 BILLION YEARS AGO
 fossilized cysts of primitive protists.
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  1.2 BILLION YEARS AGO
 numerous fossils genetic evidence suggests divergence of modern eukaryotes occurred.
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  (for scale purpose)