I II III IV Early Earth A Earth was formed about 4 6 billion years ago BYA B the rocky mantle melted as the atmospheric temperature rose C asteroids struck the planet vaporizing oceans D oceans formed from water condensation as the earth cooled E decreased CO 2 levels cooled the atmosphere F two supercontinents formed 1 Rodinia a all continents 2 Pangea a Gondwana and Laurentia Formation of Life A Archean 1 3 2 3 8 BYA 2 characterized by formation of Rodinia B Proterozoic 1 diversification of multicellular organisms a Cambrian period Fossils A formation process 1 organism buried in sediment 2 calcium in bone or other hard tissues mineralizes 3 surrounding sediment hardens to form rock B aging fossils 1 relative age a position of fossil in sediment 1 goes by age of sediment 2 absolute age a estimated by rates of radioactive decay C first cells were found to be 3 5 billion years old 1 resemble present day prokaryotes D stromatolites 1 mats of cyanobacteria that trap mineral deposits 2 oldest are 2 7 billion years old Diversification A RNA may have been first genetic material B amino acids formed proteins C metabolic pathways emerged 1 fatty acids increased the probability of metabolic reactions 2 formed cell membranes
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