Biogenesis: Origin of Life on Earth

1. Origin of Life • Biogenesis • Earth’s History • The First Life-forms

2. Biological Evolution • To View Video: • Move mouse cursor over slide title-link • When hand appears, click once • ASX Video plays about 20 min • A 10 Question Video Quiz is included in the presentation

3. Biogenesis • The Concept of Spontaneous Generation • Redi’s Experiment • Spallanzani’s Experiment • Pasteur’s Experiment

4. Learning Objectives • TSW… • Define spontaneous generation, & list some of the observations that led people to think that life could arise from nonliving things • Summarize the results of experiments by Redi & by Spallanzani that tested the hypothesis of spontaneous generation • Describe how Pasteur’s experiment disproved the hypothesis of spontaneous generation

5. Spontaneous Generation • Concept that living things could arise from non-living things • Examples • Maggots appear on rotting meat • Fish & tadpoles appear in formerly dry ponds • Biogenesis • All living things arise from other living things • Cell theory

6. Redi’s ExperimentFrancesco Redi (1626 – 1697) • Problem • How do maggot life arise in rotting meat? • Observation • Flies land on rotting meat • Maggots appear in rotting meat • Hypothesis • Maggots arise from the eggs of flies

7. Redi’s Experiment:1668 • Investigation • Control group – meat in open jars: exposed to flies • Experimental group – meat in muslin sealed jars: no contact w/ flies • Data • Meat in open jars – developed maggots • Meat in sealed jars – no maggots appear • Conclusion • Maggots hatch from fly eggs laid on rotten meat • Criticism • Did not address microorganisms

8. Spallanzani’s ExperimentLazzaro Spallanzani (1729 – 1799) • Problem • Where do microorganisms come from? • Observation • Broth exposed to air develops microorganisms & spoils • Microorganisms can be carried into the air on dust • Hypothesis • Microorganisms arise from other microorganisms

9. Spallanzani’s Experiment:1768 • Investigation • Control group – boiled broth left in open flask: exposed to dustin air • Experimental group – boiled broth in sealed flask: no exposure to dust • Data • Broth in open flasks – developed microbes • Broth in sealed flasks – no microbes appear • Conclusion • Microorganisms arise from other microorganisms • Criticism –Sealed flasks deprived of a vital force

10. Pasteur’s ExperimentLouis Pasteur (1822 – 1895) • Problem • Where do microorganisms come from? • Observation • Broth exposed to air develops microorganisms & spoils • Microorganisms can be carried into the air on dust • Hypothesis • Microorganisms arise from other microorganisms

11. Pasteur’s Experiment:1859 • Investigation • Control group – boiled broth left in open curve-necked flask: dustin air is trapped by neck • Experimental group – boiled broth is exposed by breaking necks: exposure to dust • Data • Broth in open flasks – developed no microbes for 1 year • Broth in flasks w/ broken neck – microbes appear right away • Conclusion • Microorganisms arise from other microorganisms • No Criticism – Vital force concept abandoned

12. Earth’s History • The Formation of the Earth • The First Organic Compounds • From Molecules to Cell-like Structures

13. Learning Objectives • TSW… • Outline the modern scientific understanding of the formation of Earth • Summarize the concept of half-life • Describe the production of organic compounds in the Miller-Urey experiments • Summarize the possible importance of cell-like structures produced in the laboratory

14. The Formation of the Earth • 5 by – Solar system is swirling mass of gas & dust • Inward collapse of most material: sun forms • Planets form from remainder • 4.6 by – Earth formed • 400 million year period of collisions of planetesimals • Earth is molten due to release of heat energy from collisions • Evidence from moon rocks & meteorites

15. Earth’s AgeVolcanism • 4 by – Planetesimal collisions subside • Volcanic activity begins to form primitive atmosphere • 3.8 by – Oldest known Earth rocks • Ancient atmosphere is neither oxidizing nor reducing • Gasses: CO2; N2; H2O vapor

16. Earth’s AgeLava Flow • 3.2 by – Earth cools as collisions & volcanic activity subside • Atmosphere forms from out gassing from rocks & gas capture • Oceans form from condensation of H2O from cooling surface & comet capture • 2.2 by – Earth has continents & oceans like today • Ancient atmosphere is neither oxidizing nor reducing • Gasses: CO2; N2; H2O vapor

17. Radioactive Dating • # Protons (p+) – constant for each element • Atomic number • Examples: C = 6; H = 1 • # Neutrons (n0) – variable for each element • Atomic mass number = #p+ + #n0 • Examples: C may be 12C, 13C, or 14C; H may be 1H, 2H (deuterium), or 3H (tritium)

18. Radioactive Dating • Radioactive isotopes – radioisotopes • Elements w/ unstable nuclei that undergo radioactive decay– particles are released • Half-life • Length of time for ½ of any sample of a radioisotope to decay • Half-life can vary from a fraction of a second to billions of years • Used inabsolute dating • Specific time of existence

19. Dating with Index Fossils • Index fossils • Extinct wide-spread species whose fossils can be found all over the world • Usually marine organisms • Carried world wide on ocean currents • Used inrelative dating • Fossils of a species found & dated in one region of the Earth are assumed to be the same relative age as those of the same species found in another region Extinct brachiopods

20. Experimental Synthesis: Organic Compounds • Miller-Urey Experiment (1953) • Tested Oparin’s hypothesis • Circulated H2O vapor & other gasses through chamber w/ electric sparking device • Condensed vapor into liquid water • Analyzed condensate for organic compounds • Results • Some amino acids & other organic compounds formed

21. Miller-Urey Experiment • To View Video: • Move mouse cursor over slide title-link • When hand appears, click once • ASF Video plays about 3 min

22. Experimental Synthesis: Organic Compounds • Further Experiments (1960s-1980s) • Tested Oparin’s hypothesis • Used a variety of gasses • Used a variety of energy sources • Results • All 20 amino acids • Simple mono- & di-saccharides • Fatty acids • ATP • RNA & DNA nucleotides

23. Modern StudiesSuggest Thermal Vents • Further Experiments (1990s) • Ancient atmosphere neither reducing nor oxidizing • Gasses: CO2; N2; H2O vapor • Energy sources: hot minerals • Synthesis of organics– near undersea erupting volcanoes or thermal vents • Rich in sulfur & iron compounds • Reducing conditions – H2S

24. Life at Hydrothermal Vents • To View Video: • Move mouse cursor over slide title-link • When hand appears, click once • ASF Video plays about 5 min

25. Organic Compounds from Beyond Earth • Organic compounds are abundant w/in our galaxy • Form in giant dust clouds in space • Organic compounds can be carried to earth by comets & meteorites • May have accumulated in oceans over millions of years during formation of the Earth

26. The First Organic Compounds • Oparin’s Hypothesis (1923) • Early Earth atmosphere • Reducing gasses present • NH3(ammonia); H2(hydrogen gas); H2O (water vapor); CH4(methane) • Energy source – lightning & UV radiation • Scenario: • Simple organic compounds form in atmosphere • Compounds rained into oceans • Complex organic compounds form from chemical reactions in presence of lightning & UV radiation

27. From Molecules toCell-like Structures • Protobionts • Form spontaneously in laboratory conditions from abiotically produced organic compounds • Have some life-like properties • Reproduce by budding • Exhibit metabolic ability • Microspheres • Proteins organized into a membrane • Coacervates • Linked amino acids & sugars organized into a droplet

28. The First Life-forms • The Origin of Heredity • The Roles of RNA • The First Prokaryotes • The First Eukaryotes

29. Learning Objectives • TSW… • Explain the importance of the chemistry of RNA in relation to the origin of life • List 3 inferred characteristics that describe the first forms of cellular life on Earth • Name 2 types of autotrophy & describe the difference btw them • Define endosymbiosis, & explain why it is important in the history of eukaryotes

30. HeredityReview:Transcription&Translation • Heredity & Phenotype • DNA RNA  PROTEIN • Proteins give us our individual physical appearance & physiology • Q.Why is RNA necessary? • DNA is also a template • Why not make proteins directly from DNA? • A.It probably evolved 1st • RNA is simpler & readily produced by aboitic processes • Many viruses reproduce using RNA

31. BIG-TIME QUESTION!!!Replication requires a hereditary substance. Also, replication requires proteins to catalyze the replication process. Origin of Heredity Conundrum!!!Proteins cannot be formed w/out nucleic acids. Mmmmm…but nucleic acids cannot be formed w/out proteins!

32. Heredity & RNA • Roles of RNA • Transcription & translation (per earlier chapter) • Ribozyme– RNA molecule: • Acts as an enzyme • Replicates itself • The 1st life-form MAY have been a protobiont-like “cell” w/ ribozyme-like RNA enclosed • It would contain a “genetic code” • It could replicate its hereditary material • It could evolve via natural selection • It could catalyze the synthesis of proteins • What’s not to like?

33. The First ProkaryotesSimilar to Archaebacteria • Bacteria-like Organisms (3.8+ by) • Anaerobic metabolism • Did not use O2 • Heterotrophy • Took in organic molecules from the environment • Autotrophic Life • Chemoautotrophy –chemosynthesis • Use CO2 as C source (like photoautotrophy) • Use inorganic molecules (H2S) as energy source (not sunlight)

34. Later Forms:Bacteria & Cyanobacteria • Cyanobacteria (3.8 by ?) • Photosynthesis • Uses CO2 as C source • Uses sunlight as energy source • Produces O2 as a byproduct: “Oxygen Revolution” • First fossils – 3.5 by • Look like modern cyanobacteria • Aerobic Metabolism • Evolved to absorb poisonous O2 from photosynthesizing cells • Uses O2 to “burn” sugar & produce ATP energy

35. Stromatolites& Bacterial Mats

36. The First Eukaryotes • Eukaryotes (2 – 1.5 by) • Endosymbiosis • Small prokaryotes invade larger prokaryote • Mutualism: symbiotic relationship begins • Membrane Infolding • Regions of prokaryote cell membrane loop inward & pinch off into cell interior • Membranes are metabolically dedicated to specific tasks

37. The GeologicTime Scale Time Periods • Eons(ex. Phanerozoic) • Eras(ex. Cenozoic) • Periods(ex. Quaternary) • Epoch (ex. Holocene)