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ASTR/GEOL 3300: ET Life

ASTR/GEOL 3300: ET Life. Logistics: HW 3 due Monday. HW#2 is being graded! Plan for Today: Evolution of Cells Life in Extreme Environments Ingredients of Life ). Origin of Life: Summary. “Organic soup” vs. dilute solution. Complex organics developed (mineral templates?).

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ASTR/GEOL 3300: ET Life

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  1. ASTR/GEOL 3300: ET Life • Logistics: • HW 3 due Monday. • HW#2 is being graded! • Plan for Today: • Evolution of Cells • Life in Extreme Environments • Ingredients of Life)

  2. Origin of Life: Summary • “Organic soup” vs. dilute solution. • Complex organics developed (mineral templates?). • “Pre-cells” enclosed complex organics. • Natural selection increased RNA complexity. • DNA developed within some successful cell(s). A reasonable scenario, though many details are missing!

  3. What kind of organisms are “Eukaryotes” vs. “Prokaryotes”? • All Archaea and Bacteria are Prokaryotes because they lack a distinct nucleus with a membranous compartment (some exceptions). • All Eukarya are related on the phylogenetic tree. They are big and complicated. How then did they emerge? • Thought questions: If there WAS invasive “Alien life” on Earth, would we expect it to fit on our Phylogenetic Tree?

  4. Evolution of Eukaryotes • Prokaryote membrane “infoldings” may have compartmentalized cell functions. • DNA isolated within membrane: nucleus.

  5. Evolution of Eukaryotes • Specialized prokaryotes may have developed symbiotic relationships with host cells. • Mitochondria & chloroplasts do have bacteria-like DNA!

  6. How is information about evolution preserved and interpretable, other than from molecular/genetics studies? • The Fossil Record

  7. The Fossil Record • Sediments are laid down sequentially in water. • Fossils: Minerals dissolved in water replace harderparts of dead organisms as rock. • Systematic increase of fossilcomplexity with time.

  8. Grand Canyon: 300 Myr of History

  9. The Rise of Oxygen • Banded iron formations (BIFs) ~2 – 3.9 Byr old: • Fe-rich minerals oxidize (“rust”) from O2(3Fe + 2O2 Fe3O4). • BIFs could form only before atmosphere had much O2; otherwise, enough iron would not be dissolved in oceans. • Then, Earth’s oxygen levels increased at uncertain rate…. • Photosynthesis was catching on: CO2+H2Osugar+O2: • Energy for photosynthesis is from sunlight.. BIF cyanobacteria

  10. The Cambrian Explosion • Macroscopic life diversity “exploded” ~600 Myr ago: • Oxygen levels had risen: A good energy source! • But O2 attacks organic bonds: many microbes went extinct! • Soon after several Snowball Earths: coincidence or trigger? Cambrian sea Trilobite fossil

  11. Creatures of the Cambrian • Burgess Shale, British Columbia. Hallucigenia

  12. Colonization of the Land • For macroscopic life, protective ozone (O3) layer was vital step to inhabiting land: • Shields the surface from dangerous ultraviolet sunlight. • Life generated O2 (through photosynthesis), which forms O3, which protects life!

  13. Timeline of Geology & Life on Earth Eons: Eras: Hadean: “hellish” Paleozoic: “old life” Archaean: “ancient” Mesozoic: “middle life” Proterozoic: “earlier life” Cenozoic: “recent life” Phanerozoic: “visible life”

  14. Mass Extinctions

  15. Mass Extinctions: Possible Causes • Large impacts: Random or somehow regular intervals? • Climate change from high rate of volcanism? • Magnetic field collapse allows more charged particles to hit Earth, increasing mutation rates? • Nearby supernovas eject cosmic rays, increasing mutation rates?

  16. Redox Reactions • Exchange of electrical charge between atoms or molecules during a chemical reaction, which gives off energy. • Example: H2 + 1/2 O2 H2O • The energy released by redox reactions can be used to make ATP, thus can “power” life! oxidized (loses electrons) reduced (gains electrons)

  17. Chemical Disequilibrium: Energy for Life • Photosynthesis (plants): • CO2+H2Osugar+O2 • Aerobic respiration (animals): • sugar+O2 CO2+H2O • Fermentation (anaerobic: without O2): • First microbes were probably anaerobic. • Less effective at producing energy than aerobic reactions.

  18. Examples of Other Redox Reactions That Can Power Life • Iron oxidation: • 2Fe2+ + 1/2 O2 + 2H+ 2Fe3+ + H2O • Methanogenesis: • CO2 + 4H2 CH4 + 2H2O • Sulfur reduction: • H2SO4 + 4H2 H2S + 4H2O • Sulfur oxidation (early photosynthesis): • CO2 + 2H2S  CH2O + 2S + H2O Chemical disequilibrium can drive redox reactions to power microbial life, even in the absence of sunlight.

  19. Metabolic Classifications:Carbon & Energy Sources • Photo-: Energy from sunlight. • Chemo-: Energy from chemical reactions (w/o sunlight). • Heterotroph: Carbon from existing organics (food). • Autotroph: Carbon from atmospheric CO2.

  20. Life in Extreme Environments • Extremophiles: Organisms (prokaryotic) that survive in “extreme” conditions. • Hyperthermophile • Halophile • Lithophile • Piezophile • High-temperature loving • Salt-loving • Rock-loving • Pressure-loving Antarctic endoliths Yellowstone microbes

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