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Chapter 17: The History of Life. 17.1 The Fossil Record. Paleontologist : scientist who studies fossils Fossil : preserved remains or evidence of an ancient organism Extinct : term used to refer to a species that has died out
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17.1 The Fossil Record • Paleontologist: scientist who studies fossils • Fossil: preserved remains or evidence of an ancient organism • Extinct: term used to refer to a species that has died out • Key Concept: The fossil record provides evidence about the history of life on Earth. It also shows how different groups of organisms, including species, have changed over time.
17.1 Interpreting Fossil Evidence • Relative dating: age of a fossil is determined by comparing its placement with that of fossils in other layers of rock • Index Fossils: distinct fossils found in certain layers of rock in a wide geographic range (Fig. 17-3) • Key Concept: Relative dating allows paleontologists to estimate a fossil’s age compared with that of other fossils.
17-1 Radioactive Dating • Scientists use half-lives of radioactive elements to determine the age of a sample. • Half-life: length of time required for half of the radioactive atoms in a sample to decay (Fig. 17-4) • Key Concept: In radioactive dating, scientists calculate the age of a sample based on the amount of remaining radioactive isotopes it contains
17.2 Formation of Earth • Estimated age of the earth based on geological evidence: 4.6 billion years • Key Concept: Earth’s early atmosphere probably contained hydrogen cyanide, carbon dioxide, carbon monoxide, nitrogen, hydrogen sulfide, and water.
17.2 The First Organic Molecules • Two scientists created conditions of the early Earth in the lab. After a few days, several amino acids formed. (Fig. 17-8) • Key Concept: Miller and Urey’s experiments suggested how mixtures of the organic compounds necessary for life could have arisen from simpler compounds present on a primitive Earth. “Scientists now know that Miller and Urey’s original simulations of Earth’s early atmosphere were not accurate.” (p. 424)
17.2 Free Oxygen • Early life forms were anaerobic because they lived in an oxygen-free environment. • Key Concept: 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.
17.2 Origin of Eukaryotic Cells • Endosymbiotic theory: eukaryotes formed from the symbiotic (interdependent) relationship between ancestral eukaryotes and aerobic or photosynthetic bacteria. (Fig. 17-12) • Key Concept: The endosymbiotic theory proposes that eukaryotic cells arose from living communities formed by prokaryotic organisms. • Evidence: Similarities between mitochondria, chloroplasts and bacteria. (DNA, ribosomes and binary fission)
17.3 Patterns of Evolution • Macroevolution: large-scale evolutionary patterns and processes that occur over long periods of time. • Six Topics: • Extinction: mass extinctions opened ecological opportunities for surviving organisms. (i.e. dinosaurs replaced by mammals and birds) • Adaptive radiation: many species evolving from a single or small group of species (Fig. 17-22) • Convergent evolution: different species from similar climates resemble each other (Fig. 17-23)
17.3 Patterns of Evolution • Macroevolution: large-scale evolutionary patterns and processes that occur over long periods of time. • Six Topics: (Skipped topic 6) • Coevolution: organisms closely connected by ecological interactions evolve together (Fig. 17-24) • Punctuated equilibrium: stable periods and rapid periods of evolution (Fig. 17-25) • Changes in developmental genes: expression of hox genes greatly effects development. (17-26)
