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AP BIOLOGY THE HISTORY of EARTH

AP BIOLOGY THE HISTORY of EARTH. CHAPTER 25 CAMPBELL and REECE. 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

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AP BIOLOGY THE HISTORY of EARTH

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  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: • abioticsynthesis 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) & Haldane (British) each came to conclusion early atmosphere was reducing environment (gain e-) in which organic cpds could have formed from simpler molecules

  7. 1st Organic Compounds • Energy sources: • Lightening • 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 reducing atmosphere • Added cpds considered to have been there

  9. Miller & Urey’s Experiment

  10. Miller & Urey’s Results

  11. Miller & Urey’s Results • repeated using same or similar ingredients, different recipes for the atmosphere also produced organic compounds • ?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 cpds

  12. 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

  13. Murchison Meteorite

  14. Murchison Meteorite • fell 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 cpds based on charge & size) have revealed at least 14,000 unique molecules

  15. 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)

  16. Protocells • Basic characteristics of life : reproduction & metabolism: • 1stcells 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

  17. Vesicles as 1st step? • When lipids & other organic molecules added to water  vesicles spontaneously form • lipid bilayer (separation of hydrophiloic & 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

  18. Self-Replicating RNA • RNA can act as enzyme • RNA catalysts called: ribozymes • some can make complimentary strands of short pieces of RNA  mutations  more stable &/or successful

  19. 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

  20. The Fossil Record Documents the History of Life

  21. The Fossil Record • based mostly on sequence in which fossils have accumulated in sedimentary rock strata • an incomplete record of evolutionary change (gaps still be filled in) • known fossil record biased toward species that: • survived for long periods of time • were abundant • were widespread • in certain types of environments • made of some hard parts

  22. “This could mess up the fossil record, you know.”

  23. Tiktaalik • extinct • closest relative to of 1st vertebrate to walk on land

  24. Radiometric Dating • ethodof absolute dating based on decay of radioactive isotopes (1 element  different element + some particle) • half-life = rate of decay of ½ the specimen • ½ lives are constant & characteristic to each radioactive element • outside conditions do not affect rate of decay

  25. Dating Fossils C-14 • in all living things • C-14 decays into N-14 • ½ life = 5,730 years • measure ratio of C-12 to C-14 left in fossil • can only use C-14 dating up to about 75,000 yrs old • amt of C-14 left after that so minimal that accuracy becomes an issue • if organism dead <500 yrs there to too little to date accurately

  26. The 1st Single-Celled Organisms • earliest direct evidence of life date from 3.5 billion years ago from fossilized stromatolites

  27. Stromatolites • are layered rocks that form when certain prokaryotes (cyanobacteria) bind thin fiolms of sediment together • today, found in warm, shallow salty bays • reasonable to infer that the bacteria originated much earlier ….. 3.9 billion years ago

  28. Stromatolites • early prokaryotes were Earth’s only living inhabitants from 3.5 to 2.1 billion years ago

  29. Photosynthesis & the Oxygen Revolution • most of Earth’s atmospheric oxygen is of biologic origin (photosynthesis) • at first, O2 would have stayed dissolved in water until concentration high enough to react with Fe in water. • water + iron  iron oxide (ppt) • these sediment formed banded iron formations

  30. Iron Oxide

  31. Oxygen • once all dissolved Fe ppt out of water the dissolved O2 then released as oxygen gas to atmosphere

  32. Rise of Atmospheric Oxygen

  33. Rise in Atmospheric Oxygen • began ~2.3 billion years ago • What caused the rise? probably chloroplasts • rising O2 levels would have killed off some anaerobic prokaryotes • survivors in environments with low O2 levels • Cellular Respiration may have started as adaptation to rising oxygen

  34. 1st Eukaryotes • oldest accepted eukaryotic fossils: 2.1 billion years

  35. Endosymbiont Theory • mitochondria & plastids (general term for chloroplasts & related organelles) were once prokaryotes that began living in larger host cells • endosymbiont: cell that lives w/in host cell • entered cell as undigested prey or internal parasite • symbiotic relationship has been recreated w/in 5 yrs using other cells

  36. symbiosis mutually beneficial • all eukaryotes have mitochondria but not all have plastids soooo • Hypothesis: serial endosymbiosis : mitochondria evolved b/4 plastids

  37. Evidence Supporting Endosymbiosis • inner membranes of mitochondria & plastids have enzymes & transport sytems homologous to those found in plasma membranes of living prokaryotes • mitochondria & plastids replicate like prokaryotes • each contain a single circular DNA molecule, not ass’c with histones or large amts other proteins (just like bacterial DNA)

  38. Evidence Supporting Endosymbiosis • both have ribosomes & enzymes to transcribe & translate their DNA  proteins • their ribosomes more similar to prokaryotic ribosomes than to eukaryotic cytoplasmic ones

  39. Origin of Multicellularity • 1st eukaryotes all unicellular organisms • common ancestor of multicellular organisms (based on DNA comparisons) lived ~1.5 billion years ago

  40. Early Multicellular Organisms • 1st appear in fossil record ~ 575 million yrs ago • called Ediacaran biota • soft bodied • up to 1 m in length • probably limitied in size & diversity until late Proterozoic due to series of Ice Ages which covered most of Earth’s land mass & seas 750 – 580 million years ago

  41. 640 million years ago

  42. 575 million years ago • “snowball” Earth thawed • 1st major diversification of multicellular eukaryotes • lasted until ~ 40 million years ago

  43. Cambrian Explosion

  44. b/4 Cambrian Explosion • all large animals were soft-bodied • little evidence of predation

  45. b/4 Cambrian Explosion • many animal phyla began pre-Cambrian • DNA analysis suggests most animal phyla began to diverge from each other as early as 700 million – 1 billion years ago

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