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The Origin of Life Notes: Chapter 14 The Beginning: Earth is about 4.6 billion years old Life began on Earth about 3.5 billion years ago in the ocean Evidence of Life: Fossils: remains of organisms, found in sedimentary rock Relative Dating: lower rocks are older than higher ones Radiometric Dating: using radioactive isotopes in rocks because rate of decay is related to half-life Relative Dating: Radiometric Dating: How does life arise? Spontaneous generation: life from nonliving things – Francesco Redi: disproved theory by showing that flies must come from other flies How does life Arise? Spontaneous generation: – Louis Pasteur: concluded that microorganisms must come from other microorganisms using Sshaped flasks that let in only air = no organisms Biogenesis: life only from other living things – Miller & Urey: showed that organic molecules could have formed the beginning of life The origin of cells: Anaerobic prokaryotes: lived in an atmosphere with no oxygen The origin of cells: Aerobic organisms: evolved once photosynthesis released oxygen The origin of cells: Prokaryotes: cells without a nucleus or organelles Eukaryotes: cells with a nucleus and organelles – cells grew in complexity once conditions for life improved