AP BIOLOGY THE HISTORY of EARTH

1. AP BIOLOGYTHE HISTORY of EARTH CHAPTER 25 CAMPBELL and REECE

2. Conditions on early Earth made the Origin of Life possible • Macroevolution : evolutionary change above the species level • examples: • emergence of terrestrial vertebrates • mass extinctions impact on diversity of life • origin of key adaptations like flight in birds

3. Where did 1st cell come from? • 4 main stages could have produced very simple cells: • The abiotic synthesis of small organic molecules • Joining of these small molecules into macromolecules (proteins, nucleic acids) • Packaging of these macromolecules into protocells, droplets with membranes that maintained internal chemistry different from their surroundings • Origin of self-replicating molecules that eventually made inheritance possible

4. Synthesis of Organic Cpdson early Earth • Planets of our solar system formed ~ 4.6 billion yrs ago • 1st few hundred million yrs conditions would not have allowed life on Earth

5. 1st Atmosphere • Collisions would have vaporized any water preventing seas from forming • Atmosphere thick with gases released from volcanic activity

6. 1st Atmosphere • 1920’s: Oparin (Russian chemist) and Haldane (British scientist) each came to conclusion early atmosphere was reducing environment (gain e-) in which organic compounds could have formed from simpler molecules

7. 1st Organic Compounds • Energy sources: • Lightning • Thermal energy • Intense UV radiation

8. Primordial Soup • Haldane had hypothesized the early seas site of 1st organic compounds  1st cells • Miller & Urey (Univ. of Chicago) in 1950’s • Tested Oparin & Haldane ‘s premise • Created a reducing atmosphere • Added compounds considered to have been found existing on early earth (hydrogen gas – H2, ammonia – NH3, methane – CH4, and H2O vapor)

9. Miller & Urey • Experiment: In 1953, Stanley Miller set up a closed system to simulate conditions thought to have existed on early Earth • Water mixture in “sea” flask was heated; vapor entered atmosphere flask • “Atmosphere” flask contained mix of hydrogen gas, methane, ammonia, and water vapor (believed to mimic early Earth’s atmosphere) • Sparks were discharged to mimic lightning • Condenser cooled the “atmosphere”, “raining” water and any dissolved molecules down into sea flask • As material cycled through apparatus, Miller periodically collected samples for analysis • Results: Miller identified variety of organic molecules common in organisms (including simple molecules like formaldehyde (CH2O) and hydrogen cyanide (HCN) and more complex molecules (like amino acids and hydrocarbons) • Conclusion: Organic molecules (a 1st step in the origin of life) may have been synthesized abiotically on early Earth

10. Miller & Urey’s Experiment

11. Miller & Urey’s Results

12. Miller-Urey Experiment Clip

13. Miller & Urey’s Results • Have been repeated using same or similar ingredients, different recipes for the atmosphere and they also produced organic compounds • Still ?s about amounts of methane, ammonia (was there really enough to make it a reducing environment?) • Some repeated experiment in non-reducing, non-oxidizing conditions & still produce organic compounds

14. Miller-Urey Experiment demonstrates: • Abiotic synthesis of organic molecules is possible under various assumptions about the composition of Earth’s early atmosphere • Meterorites may also have been source of minerals and organic molecules • Contain amino acids, lipids, simple sugars, uracil

15. Murchison Meteorite

16. Murchison Meteorite • Fell to Earth in so named town in Australia in 1969 • large (100 kg) and was quickly retrieved • 2010 article published in Scientific American: results of mass spectrometry (separating compounds based on charge & size) have revealed at least 14,000 unique molecules

17. Abiotic Synthesis of Macromolecules • 2009 study showed the abiotic synthesis of RNA monomers can occur spontaneously from simpler precursor molecules • Drip solutions with amino acids (aa) or RNA nucleotides onto hot sand, rock, or clay  polymers of aa & RNA (w/out using enzymes or ribosomes)

18. Protocells (Protobionts) • Basic characteristics of life : reproduction & metabolism: • So 1st cells would have had to be able to reproduce which would have required them to have a source of nitrogenous bases, sugars, phosphate groups • Now complex enzymes make this all happen

19. Vesicles as 1st step? • When lipids & other organic molecules added to water  vesicles spontaneously form • lipid bilayer (separation of hydrophilic & hydrophobic molecules) • These abiotically produced vesicles “reproduce” and grow on their own. • Clay, like from early Earth will be absorbed into the vesicles • some vesicles demonstrate semi-permeability

20. Self-Replicating RNA • RNA (when folded)can act as enzyme • RNA catalysts called: ribozymes • Some can make complimentary strands of short pieces of RNA  mutations  more stable &/or successful

21. Ribozyme • Once self-replicating RNA possible much easier for further changes to happen. • Once double-stranded DNA appeared it would have been more stable so RNA left with role we see today