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Origin of Life on Earth

Origin of Life on Earth. Reading Assignment. “Origin of Life on Earth” From: The Search for Life on Other Planets by Bruce Jakosky, 1998, pp. 93–109 (back of course packet) SETI Module ( “ Topics”  “Search for Life”) Optional: “The Beginnings of Life on Earth” by Christian de Duve

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Origin of Life on Earth

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  1. Origin of Life on Earth

  2. Reading Assignment • “Origin of Life on Earth”From: The Search for Life on Other Planets by Bruce Jakosky, 1998, pp. 93–109 (back of course packet) • SETI Module • ( “Topics”  “Search for Life”) • Optional: “The Beginnings of Life on Earth” by Christian de Duve • American Scientist, September-October 1995 • http://www.sigmaxi.org/amsci/articles/95articles/cdeduve.html

  3. Chronology • Solar system, incl. Earth, formed about 4.6 BYA (inhospitable* to life for first 0.6 BY) • Complex life on Earth existed by ~3.8 BYA • Evidence: microfossils of bacteria (radiodated) • Therefore life appeared quickly (inevitably?) *severe asteroid bombardment

  4. Abiotic (or Prebiotic) Chemistry • Abiotic = no life • Prebiotic = before life • Miller & Urey experiment • Lab simulation of early conditions on Earth (?) • Produced amino acids, and later purines and pyrimidines(DNA/RNA building blocks), and sugars

  5. Miller & Urey Experiment Reconsider assumptions (N2 & CO2vs. H2, CH4, & NH3)

  6. Life (or Precursors) From Space? • Murchison Meteorite • Australia 1969 • Asteroid or comet fragment • Amino acids • Organic acids • Interstellar dust • Incl. formaldehyde (H2CO), hydrogen cyanide (HCN), acetaldehyde (C3H4O), etc. • Mars rock from Antartica • Organic compounds • Polycyclic aromatic hydrocarbons (PAH’s) • Microfossils???

  7. “RNA World” Hypothesis • Among DNA, RNA, & proteins, it is assumed that RNA came first (but not as the first biomolecule!) • Some RNAs are now known to have enzyme functionality: “ribozymes” • e.g. in protozoan Tetrahymena (& in ribosomes!) • Intron self-splicing (“genes in pieces”) — later • DNA replication etc. requires (protein) enzymes • So maybe RNA could have served as genetic material, and managed both self-replication and protein synthesis • dual role of RNA: information & catalysis Recall: 3 standard types: mRNA, tRNA, & rRNA

  8. A Ribozyme

  9. RNA  protein

  10. Evolution in RNA World • Self-replication of genetic information in RNA, with inevitable copying errors (heritable variation), would have (further) unleashed evolution by natural selection in changing environments faced by early forms of life on Earth.

  11. Beyond Origins • Life essentials • self-organization, spatial containment of functions, behavior, reproduction, and evolution (change) • Protocells • Protometabolism

  12. AstrobiologyWhere Else to Look • In our solar system • Mars • Titan (moon of Saturn) • Europa (moon of Jupiter) • Planets elsewhere

  13. Rare Earth? • New book out: • Rare Earth: Why Complex Life is Uncommon in the Universe • by Peter Ward & Donald Brownlee (Copernicus, 2000) • Earth is rather special • Composition, temperature, & stability unusual • Moon stabilizes Earth’s tilt (seasons) • Jupiter absorbs or deflects asteroids, comets, etc. • Plate tectonics promote evolution & diversity • Far away from unstable galactic center • Elsewhere • Excessive radiation & impacts, “wrong” chemical mix (e.g., low metal abundance  wimpy planets), more highly elliptical orbits, …

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