The Origin and Early Evolution of Life Chapter 18
Learning Objectives • Differentiate between chemical evolution and organic evolution. • Describe the conditions on the primitive earth predicted by laboratory experiments that favored the spontaneous development of organic molecules. • Explain the probable sequence in the origin of the first cells, and describe how this cell interacted with its environment. • Review the theories proposed to explain the origin of eukaryotic organelles.
The Big Bang • 12-15 billion years ago all matter in the universe was compressed into a mass the size of our sun • Sudden instantaneous explosion of matter and energy throughout the known universe
p. 288 Earth Forms • About 4.6 to 4.5 billion years ago • Minerals and ice orbiting the sun started clumping together • Heavy minerals moved to Earth’s interior, lighter minerals floated to surface • Produced outer crust and inner mantle • Chemical evolution produced the primordial sea and the early atmosphere that would support the biosphere of the future.
The Planet: If smaller in diameter, gravity would not be great enough to hold onto atmosphere If closer to sun, water would have evaporated If farther from sun, water (the solvent of life) would have been locked up as ice Early Atmosphere: Hydrogen gas Nitrogen Carbon monoxide Carbon dioxide No gaseous oxygen Earth Is “Just Right” for Life p. 288
Stanley Miller’s Experiment • Mixed methane, hydrogen, ammonia, and water • Simulated lightning • Amino acids and other small molecules formed What, at a minimum, is needed to form a cell-like structure from these molecules? p. 289
Possible Sequence p. 291 END “Organic Evolution” Why is RNA believed to be the first genetic information? Why is DNA a better molecule for heredity? informational molecules separation of environments START: “Chemical Evolution”
The First Cells • Prokaryotic heterotrophs Describe what this means. • Secured energy through anaerobic metabolism …Describe. • No oxygen present …Why not? Is there fossil evidence for these first cells? p. 291
Fossil Evidence • photosynthetic eubacteria • Oxygen producing • permits aerobic respiration 3.5 bya 2.1 bya 1.2 bya p. 292
Possible Origin of ER & Nuclear Envelope p. 294 aka: Autogenous Theory
Endosymbiotic Theory p. 295 Cyanophora paradoxa