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Chapter 20 : Life’s Origin & Early Evolution

Chapter 20 : Life’s Origin & Early Evolution. Looking for Life in All the Odd Places. Fig. 20-1a, p.318. Fig. 20-1b, p.318. Looking for Life in All the Odd Places. Fig. 20-2, p.319. The Big Bang. Fig. 20-3, p.320. The Big Bang Theory.

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Chapter 20 : Life’s Origin & Early Evolution

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  1. Chapter 20: Life’s Origin & Early Evolution

  2. Looking for Life in All the Odd Places Fig. 20-1a, p.318

  3. Fig. 20-1b, p.318

  4. Looking for Life in All the Odd Places Fig. 20-2, p.319

  5. The Big Bang Fig. 20-3, p.320

  6. The Big Bang Theory • 12-15 billion years ago all matter was compressed into a space the size of our sun • Sudden instantaneous distribution of matter and energy throughout the known universe

  7. Archeon Eon and Earlier • 4,600 mya: Origin of Earth • 4,600 - 3,800 mya • Formation of Earth’s crust, atmosphere • Chemical and molecular evolution • First cells (anaerobic bacteria)

  8. Earth Forms • About 4.6 and 4.5 billion years ago • Minerals and ice orbiting the sun started clumping together • Heavy metals moved to Earth’s interior, lighter ones floated to surface • Produced outer crust and inner mantle

  9. Earth Is “Just Right” for Life • 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

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

  11. First Atmosphere Fig. 20-4a, p.321

  12. First Atmosphere Fig. 20-4b, p.321

  13. Origin of Organic Compounds • Amino acids, other organic compounds can form spontaneously under conditions like those on early Earth • Compounds may have formed due to events like lightning, volcanoes, asteroid impacts

  14. Chemical Evolution chlorophyll a • Spontaneous formation of porphyrin rings from formaldehyde • Components of chlorophylls and cytochromes formaldehyde porphyrin ring system Fig. 20-5, p. 322

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

  16. Proto-Cells • Microscopic spheres of proteins or lipids can self assemble • Tiny sacs like cell membranes can form under laboratory conditions that simulate conditions in evaporating tidepools

  17. Proto-Cells Fig. 20-6b, p.322

  18. Proto-Cells Fig. 20-6c, p.322

  19. Stepped Art living cells membrane-bound proto-cells self-replicating system enclosed in a selectively permeable, protective lipid sphere enzymes and other proteins DNA RNA formation of protein-RNA systems, evolution of DNA formation of lipid spheres spontaneous formation of lipids, carbohydrates, amino acids, proteins, nucleotides under abiotic conditions Fig. 20-7c, p.323

  20. Cambrian: Explosion of Life • Origin of photosynthetic Eubacteria • Noncyclic pathway first • Cyclic pathway next • Oxygen accumulates in atmosphere • Origin of aerobic respiration

  21. The First Cells • Originated in Archeon Eon • Were prokaryotic heterotrophs • Secured energy through anaerobic pathways • No oxygen present • Relied on glycolysis and fermentation

  22. Prokaryotes Fig. 20-8a, p.324

  23. Prokaryotes Fig. 20-8c, p.324

  24. Prokaryotes Fig. 20-7, p.324

  25. Eukaryotes • The rise of Eukaryotes was thought to have stemmed from prokaryotes

  26. Eukaryotes Fig. 20-9a, p.325

  27. Eukaryotes Fig. 20-9b, p.325

  28. Advantages of Organelles • Nuclear envelope may have helped to protect genes from competition with foreign DNA • ER channels may have protected vital proteins DNA infolding of plasma membrane Fig. 20-10, p. 326

  29. DNA infolding of plasma membrane Fig. 20-10a, p.326

  30. Theory of Endosymbiosis • Mitochondria and chloroplasts are the descendents of free-living prokaryotic organisms • Prokaryotes were engulfed by early eukaryotes and became permanent internal symbionts • Chloroplasts and Mitochondria have their own DNA

  31. Theory of Endosymbiosis photosynthetic organelle that resembles a cyanobacterium mitochondrion nucleus Fig. 20-11b, p.327

  32. hydrogen-rich anaerobic atmosphere atmospheric oxygen, 10% archaean lineage d ancestors of eukaryotes h endomembrane system and nucleus noncyclic pathway of photosynthesis f cyclic pathway of photosynthesis e b origin of prokaryotes a gaerobic respiration 3.8 billion years ago 3.2 billion years ago 2.5 billion years ago Fig. 20-12a, p.328

  33. atmospheric oxygen, 20%; the ozone layer slowly develops korigin of animals j origin of eukaryotes, the first protists korigin of fungi i endosymbiotic origin of mitochondira korigin of lineage leading to plants j endosymbiotic origin of chloroplasts Aerobic species becomes endosymbiot of anaerobic forerunner of eukaryotes. 1.2 billion years ago 900 million years ago 435 million years ago Fig. 20-12b, p.328

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