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The Origin and Evolution of Life Starr/Taggart’s Biology: The Unity and Diversity of Life, Chapter 21 9e Key Concepts: Life originated more than 3.8 billion years ago All of the compounds necessary for life could have formed spontaneously under conditions that existed on the early Earth The history of life spans five intervals of geologic time Key Concepts: Divergence led to two prokaryotic lineages and to the eukaryotic divergence A theory of endosymbiosis helps explain the profusion of specialized organelles All of the kingdoms are characterized by persistence, extinctions, and radiations Certain environmental insults have had profound impacts on the direction of evolution Conditions on the Early Earth 4.5 billion years ago “Cloud” began to condense 4 billion years ago Crust and mantle formed Primitive atmosphere H2, N2, CO, CO2 , probably no O2 Hot temperatures Early Earth Primitive atmosphere H2 N2 CO CO2 Probably no O2 Synthesis of Organic Compounds Stanley Miller’s experiment Methane, hydrogen, ammonia and water in a reaction chamber Simulated lightning Amino acids and small organic compounds formed Synthesis of Organic Compounds Emergence of the First Living Cells Metabolism Natural assembly of enzymes, ATP and other organic compounds Chemical interactions A + B -------> C -------> D enzyme enzyme Origin of Porphyrin Ring Structure In chlorophyll and cytochromes In energy-yielding pathways Emergence of the First Living Cells Self Replicating Systems RNA DNA Plasma Membranes Proto-cells Origin of Prokaryotic and Eukaryotic Cells Where Did Organelles Come From ? Membranous enclosures Nucleus ER Endosymbiosis Mitochondria Chloroplasts Both have self-replicating DNA, divide independently of cell Endosymbiosis Life In the Paleozoic Era Periods Cambrian Ordovician Silurian Devonian Carboniferous Permian All six kingdoms in the seas Land plants and animals arise Life in the Paleozoic Cambrian 550-500 mya Land masses dispersed near equator Simple marine communities Origin of animals with hard parts Ordovician 500-435 mya Gondwana drifts south Major radiations of marine inverbrates and fishes Life in the Paleozoic Ordovician-Silurian boundary 435 mya First known ice age First known global mass extinction Silurian and Devonian eras Vascular plants arise Origin of amphibians Life in the Paleozoic Silurian swamp Dominated by nonvascular plants Forerunners of modern ferns and club mosses Life in the Paleozoic Devonian-Carboniferous boundary Sea levels change dramatically Mass extinction Carboniferous 360-290 mya Radiations of insects, amphibians Origins of reptiles Spore-bearing plants dominant Life in the Paleozoic Permian 290-240 mya Radiation of reptiles and gymnosperms Closed with greatest mass extinction Land masses collided to form Pangea More than 50% of families disappeared Only 5% of known species survived Life in the Mesozoic Era Periods Triassic Jurassic Cretaceous Pangea began to break up Continental drift Divergence and Speciation Major adaptive radiations Life in the Mesozoic Angiosperms arose in the late Jurassic or early Cretaceous. Adaptive radiation made them dominant plants in land environments Rise of the Ruling Reptiles Dinosaurs Arose early in the Triassic Weren’t dominant until after mass extinction Adaptive radiation Two Hypotheses for Dinosaur Extinction Asteroid Impact Theory Global Broiling Theory Last Few Seconds of the Cretaceous Life in the Cenozoic Era Present era Geological shift Shifts in climate Adaptive radiation of mammals Tropical forests Woodlands Grasslands Species diversity In Conclusion The Big Bang is a model of the origin of the universe Every element of the solar system and of life is a product of the physical and chemical evolution of the universe Four billion years ago, the Earth formed The primitive atmosphere consisted of H2, N2 , CO, and CO2 In Conclusion After the crust cooled, water accumulated and seas developed Many experiments have yielded indirect evidence that life originated under conditions prevalent on the early Earth Life originated about 3.8 billion years ago Major changes in the Earth’s crust, atmosphere, and oceans have influenced life In Conclusion Discontinuities in the fossil record mark the time of global mass extinction The first living cells were prokaryotes Divergence led to the evolution and to the ancestor of the Archaebacteria and Eukaryotes Ozygen began to accumulate in the atmosphere during the Proterozoic In Conclusion Oxygen in the atmosphere served as a selective pressure, bringing about the spontaneous formation of organic molecules Aerobic respiration was a key step towards the origin of eukaryotic cells Mitochondria and chloroplasts probably evolved as an outcome of endosymbiosis In Conclusion Ozone developed as a product of an O2 rich atmosphere. Ozone protects against ultraviolet radiation Many events brought on pulses of mass extinctions and adaptive radiations developed by M. Roig
