<P> The oldest known fossilized prokaryotes were laid down approximately 3.5 billion years ago , only about 1 billion years after the formation of the Earth 's crust . Eukaryotes only appear in the fossil record later , and may have formed from endosymbiosis of multiple prokaryote ancestors . The oldest known fossil eukaryotes are about 1.7 billion years old . However , some genetic evidence suggests eukaryotes appeared as early as 3 billion years ago . </P>
<P> The oldest known fossilized prokaryotes were laid down approximately 3.5 billion years ago , only about 1 billion years after the formation of the Earth 's crust . Eukaryotes only appear in the fossil record later , and may have formed from endosymbiosis of multiple prokaryote ancestors . The oldest known fossil eukaryotes are about 1.7 billion years old . However , some genetic evidence suggests eukaryotes appeared as early as 3 billion years ago . </P>
when did prokaryotic cells first appear on earth
when did prokaryotic cells first appear on earth
approximately 3.5 billion years ago
approximately 3.5 billion years ago