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17 The History Of Life Slide 1 of 40 Copyright Pearson Prentice Hall End Show 17-1 The Fossil Record Interpreting Fossil Evidence Relative dating allows paleontologists to estimate a fossil's age compared with that of other fossils. Index fossils are used to compare the relative ages of fossils. An index fossil is a species that is recognizable and that existed for a short period but had a wide geographic range. Slide 2 of 40 Copyright Pearson Prentice Hall End Show 17-1 The Fossil Record Interpreting Fossil Evidence Radioactive dating is the use of half-lives to determine the age of a sample. A half-life is the length of time required for half of the radioactive atoms in a sample to decay. Copyright Pearson Prentice Hall In radioactive dating, scientists calculate the age of a sample based Slide on the amount of 3 of 40 remaining radioactive End Show isotopes it contains. 17-1 The Fossil Record The First Organic Molecules Miller and Urey’s Experiment Mixture of gases simulating atmosphere of early Earth Spark simulating lightning storms Condensation chamber Water vapor Cold water cools chamber, causing droplets to form. Liquid containing amino acids and other organic compounds large organic molecules form tiny bubbles called proteinoid Slide 4 of 40 microspheres. Copyright Pearson Prentice Hall End Show 17-1 The Fossil Record Origin of Eukaryotic Cells The rise of oxygen in the atmosphere drove some life forms to extinction, while other life forms evolved new, more efficient metabolic pathways that used oxygen for respiration Endosymbiotic Theory Ancient Prokaryotes Chloroplast Aerobic bacteria Nuclear envelope evolving Ancient Anaerobic Prokaryote Photosynthetic bacteria Plants and plantlike protists Mitochondrion Primitive Aerobic Eukaryote Primitive Photosynthetic Eukaryote Animals, fungi, and non-plantlike protists Slide 5 of 40 Copyright Pearson Prentice Hall End Show