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The Origin and Early Evolution of Life

The Origin and Early Evolution of Life

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The Origin and Early Evolution of Life

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  1. The Origin and Early Evolution of Life Lecture 19

  2. The Big Bang • 12-15 (13.8) billion years ago all matter was compressed into a space the size of? • Our Galaxy • Our Solar System • Our Plant • Our Atom • Sudden instantaneous distribution of matter and energy throughout the known universe

  3. Timeline • 4.6 to 3.8 billion years ago - Leads to solid crust • 3.8 Water forms • 2.8 to 3.2 - Life starts as prokaryotic cells • 1.5 Eukaryotic cells develop • 545 Cambrian explosion • 500 Fish • 350 Amphibians • 300 Reptiles • 1.6 humans

  4. Timeline: Archaean Eon and Earlier • 4,600 mya: Origin of Earth • 4,600 - 3,800 mya (about 800 million years) • Formation of Earth’s crust, atmosphere… • Formation of the Moon • Chemical and molecular evolution only • Then came the First cells (anaerobic bacteria)

  5. Earth Forms • About 4.6 billion years ago • Gas, Minerals and ice orbiting the sun started clumping together • Heavy metals moved to Earth’s interior, lighter ones floated to surface • Iron core • Produced outer crust and inner mantle

  6. First Atmosphere • Hydrogen gas • Nitrogen • Carbon monoxide • Carbon dioxide • No gaseous oxygen

  7. Earth Is “Just Right” for Life • IF…Earth was; • Smaller in diameter, gravity would not be great enough to hold onto atmosphere • Closer to sun, water would have evaporated • Farther from sun, water would have been locked up as ice

  8. Stanley Miller’s Experiment • Mixed methane, hydrogen, ammonia, and water • Simulated lightning • Amino acids and other small molecules formed Animation

  9. How Did Cells Originate? • In the first 600 million years or so of Earth history, enzymes, ATP, and other crucial organic compounds probably assembled spontaneously - nothing came of it! • Then, by a still disputed mechanism, the concoction came together randomly to make some primitive organic molecule…

  10. Possible Sequence

  11. RNA World • DNA is genetic material now • DNA-to-RNA-to-protein system is complex! • RNA may have been first genetic material • RNA can assemble spontaneously • How switch from RNA to DNA might have occurred is not known

  12. The First Cells • Originated in Archaean Eon • There were prokaryotic cells • These were heterotrophs • Secured energy through anaerobic pathways • No oxygen present, therefore they must have • Relied on glycolysis and fermentation only!

  13. Proterozoic Eon • FIRST • Origin of photosynthetic eubacteria, as a result… • SECOND • Then, Oxygen accumulates in atmosphere, and • THIRD • Origin of aerobic respiration

  14. Advantages of Organelles • Nuclear envelope may have helped to protect genes from competition with foreign DNA • ER channels may have similarly protected vital proteins • …

  15. Possible Origin of ER

  16. Theory of Endosymbiosis • Lynn Margulis • Mitochondria and chloroplasts are the descendents of free-living prokaryotic organisms • Prokaryotes were engulfed by early eukaryotes and became permanent internal symbionts • http://www.sumanasinc.com/webcontent/anisamples/nonmajorsbiology/organelles.html

  17. Evolutionary Tree

  18. Evolutionary Tree