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Origin of Life on Earth Characteristics of Early Life Self-Replication

Origin of Life on Earth Characteristics of Early Life Self-Replication Proteins aren’t self-replicating RNA may carry out catalytic functions Ribozyme – Autocatalytic RNA RNA may have been first informational molecule DNA more stable; may have arisen from RNA Nutrition

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Origin of Life on Earth Characteristics of Early Life Self-Replication

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  1. Origin of Life on Earth • Characteristics of Early Life • Self-Replication • Proteins aren’t self-replicating • RNA may carry out catalytic functions • Ribozyme – Autocatalytic RNA • RNA may have been first informational molecule • DNA more stable; may have arisen from RNA • Nutrition • First cells likely heterotrophic • No free oxygen in atmosphere of early earth • First heterotrophs probably used anaerobic fermentation (less efficient than aerobic metabolism) • First autotrophs may have used hydrogen sulfide (H2S) as hydrogen source (modern purple & green sulfur bacteria still get H from H2S) • First autotrophs to split water for H probably ancestors of modern cyanobacteria (3.1 – 3.5 bya) • Production of O2 had profound effects

  2. Origin of Life on Earth • Characteristics of Early Life • Aerobes • O2 abundant by 2.5 bya • Replaced obligate anaerobes in most areas • Aerobic metabolism much more efficient than anaerobic metabolism • Stabilized concentrations of O2 and CO2 in atmosphere • Development of ozone (O3) layer • Eukaryotes • Appeared ~2.1-2.2 bya • How might eukaryotes have arisen from prokaryotes? • Organelles (mitochondria, chloroplasts) may have originated from symbiotic relationships between prokaryote species • Chloroplasts closely related to cyanobacteria • Mitochondria closely related to alpha proteobacteria • Serial endosymbiosis

  3. Fig. 25.8

  4. Origin of Life on Earth • Characteristics of Early Life • Aerobes • O2 abundant by 2.5 bya • Replaced obligate anaerobes in most areas • Aerobic metabolism much more efficient than anaerobic metabolism • Stabilized concentrations of O2 and CO2 in atmosphere • Development of ozone (O3) layer • Eukaryotes • Appeared ~2.1-2.2 bya • How might eukaryotes have arisen from prokaryotes? • Organelles (mitochondria, chloroplasts) may have originated from symbiotic relationships between prokaryote species • Chloroplasts closely related to cyanobacteria • Mitochondria closely related to alpha proteobacteria • Serial endosymbiosis

  5. Fig. 25.9

  6. Fig. 25.9

  7. Fig. 25.9

  8. Origin of Life on Earth • Characteristics of Early Life • Eukaryotes • Evidence for serial endosymbiosis • Inner membranes of plastids & mitochondria have enzymes and transport systems similar to those of plasma membranes in modern bacteria • Plastids & mitochondria replicate by binary fission process similar to that of bacteria • Plastids & mitochondria each contain single, circular DNA molecule without histones or other proteins (similar to bacteria) • Plastids & mitochondria have ribosomes that resemble prokaryotic more than cytoplasmic ribosomes (size, sequence, sensitivity to antibiotics)

  9. Geological Record • Rocks, sediments, fossils – Occur in layers (strata) • Oldest fossils – Stromatolites from 3.5 bya

  10. Geological Record • Dating • Index Fossils • Based on common species • Useful for establishing relative ages • Used by petroleum industry • Radiometric Dating • Technique for absolute dating • Based on decay of radioactive elements in rocks

  11. Fig. 25.5

  12. Geological Record • Dating • Index Fossils • Radiometric Dating • Half-life unaffected by temperature, pressure, etc. • Ex:40K 40Ar with t0.5 = 1.3 billion years • Initial rock has 100% 40K and no 40Ar • Rock with 40K:40Ar = 1:1 is 1.3 billion years old • Rock with 40K:40Ar = 1:3 is 2.6 billion years old • Commonly used radioisotopes • 40K with t0.5 = 1.3 billion years • 235U with t0.5 = 704 million years • 14C with t0.5 = 5730 years

  13. Geological Record • Geological Time Scale • Earth’s history divided into periods based on major geological, climatic, & biological changes

  14. Mass Extinction (K-T) First Bird (150 mya) ? Mass Extinction (96% of marine spp.) First Amniote Egg ? ”Age of Fishes” First Land Plants/Animals ? First Fishes

  15. - Siberian Volcanism - Increased CO2 - Altered Ocean Mixing Fig. 25.15

  16. Cretaceous Mass Extinction Fig. 25.16

  17. Time Scale: One Year Homo appears: Dec 31 @ 5 pm Fig. 25.7

  18. Global Plate TectonicsJurassic to Present Day By L.A. Lawver, M.F. Coffin, I.W.D. Dalziel L.M. Gahagan, D.A. Campbell, and R.M. Schmitz 2001, University of Texas Institute for Geophysics February 9, 2001

  19. Earth – Future Drift

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