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Chapter 17 The History of Life Interpreting Fossil Evidence • Fossils have been hidden in layers of rocks for millions of years • Mostly found in sedimentary rock – Can be exposed due to • shifting earth layers • Erosion from wind, rain, and running water Relative Dating • Order of appearance – Age of fossil is determined by comparing its Younger placement with that of fossils in other layers • Not precise, but allows paleontologists to estimate fossils age by comparing with other fossils Older Radioactive Dating • Radioactive elements decay at a constant rate – Measured in units called half life – Half life = length of time required for half of radioactive atoms in sample to decay • Use radioactive decay to assign absolute ages to rocks • Scientists calculate age of a sample based on amount of remaining radioactive isotopes it contains How did life begin? • Miller/Urey experiment – 1950’s – Tried to simulate conditions on early earth in lab setting • Filled flask with.. – Hydrogen, methane, ammonia, and water » Represented atmosphere • Passed electric sparks though mixture to simulate lightening • WHAT DO YOU THINK HAPPENED? Miller/Urey continued…. • Over a few days… – Several amino acids formed! • Building blocks of proteins • Suggested how mixtures of organic compounds necessary for life could have arisen from simpler compounds present on primitive Earth. Tuesday April 23rd • Which process is more accurate? –Carbon dating or –Relative dating Patterns of Evolution • Macroevolution – Large scale evolutionary patterns/processes that occur over long periods of time Extinction • More than 99% of all species ever lived are now extinct • Mass extinctions have wiped out entire ecosystems • Can be caused by – Ice ages – Meteorite – Over time, just happens Adaptive Radiation • Single species or small groups of species evolve through natural selection into diverse forms that live in different ways. – Ex. Darwin’s finches • More than a dozen evolved from single species Convergent evolution • Adaptive radiation can have “side effects” • Convergent evolution – Process by which unrelated organisms come to resemble one another • Swimming animals –Sharks, dolphins, penguins Coevolution • Process by which 2 species evolve in response to changes in each other over time Punctuated Equilibrium • Describes pattern of long, stable periods interrupted by brief periods of more rapid change – Occur when… • Small populations become isolated from main population • Small group migrates to new environment – Suggested that new species are produced by periods of rapid change. • Controversial among biologists Developmental genes and Body Plans • Developmental genes – Some determine which parts of embryo become front, rear, top, or bottom – Some determine size and shape of legs or wings • Changes in expression of developmental genes may explain how differences evolved in animals. Endosymbiotic theory • Eukaryotic cells arose from living communities formed by prokaryotic organisms GET IN MY BELLY! Prokaryotic cell Poor, helpless little victim, about to become engulfed! Warm UP – Nov. 21st • Describe convergent evolution