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 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 • 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 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 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 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: • 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

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

25. Radiometric Dating • Method of 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

26. 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

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

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

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

32. 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

33. Iron Oxide

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

35. Rise of Atmospheric Oxygen

36. 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

37. 1st Eukaryotes • oldest accepted eukaryotic fossils: 2.1 billion years

38. 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

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

41. 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)

42. 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

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

45. 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

46. 640 million years ago

47. 575 million years ago • “snowball” Earth thawed • 1st major diversification of multicellular eukaryotes • lasted until ~ 40 million years ago

48. Cambrian Explosion

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

50. 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