Ch. 17 The History of Life

1. Ch. 17 The History of Life 17.1 How Did Life Begin? 17.2 What Were the Earliest Organisms Like?

2. 17-1 How Did Life Begin? A. Pre-Darwinian thought held that all species were simultaneously created by God a few thousand years ago B. Until 19th century, most people believed in spontaneous generation (abiogenesis) where new organisms sprang up from both non-living matter.

3. 17-1 How Did Life Begin? • Spontaneous generation advocates believed • Maggots were thought to arise from decaying meat • Microbes were thought to arise from broth • Mice were thought to arise from mixtures of sweaty shirts and wheat • Francesco Redi (1668) disproved maggots-from-meat idea • No maggots developed when he kept flies away from uncontaminated meat

4. 17-1 How Did Life Begin?

5. 17.1 How Did Life Begin • Louis Pasteur and John Tyndall (mid 1800s) disproved broth-to-microorganisms idea • Microorganisms didn’t appear in the sterile broth unless the broth was 1st exposed to existing microorganisms • Experiment demolished the notion of spontaneous generation but didn’t address how life on Earth originated in the first place

6. 17.1 How Did Life Begin The broth in a flask is boiled to kill preexisting microorganisms The long, S-shaped neck allows air, but not microorganisms to enter the flask If the neck is later broken off, outside air can carry microorganisms into the broth

7. 17.1 How Did Life Begin http://education-portal.com/academy/lesson/the-origin-of-life-on-earth-theories-and-explanations.html#lesson (good intro to Primordial soup and Oparin and Mill-Urey Exp) • Alexander Oparin and John Haldane showed that spontaneous generation formation of complex organic molecules necessary for life would NOT be permitted in today’s oxygen-rich atmosphere • Oxygen reacts with other molecules breaking chemical bonds • An oxygen-rich environment tends to keep molecules simple

8. 17.1 How Did Life Begin ammonia (NH3) hydrogen gas (H2) water vapor (H2O) methane gas (CH4) EARLY EARTH CONDITIONS high temperatures frequent volcanoes electrical storms comets

9. 17.1 How Did Life Begin • The first living things arose from non-living ones • Organic molecules can form spontaneously under prebiotic (before life) conditions • Stanley Miller and Harold Urey (1953) designed an experiment that simulated prebiotic evolution • http://www.ucsd.tv/miller-urey (online Miller-Urey Activity) • Simulated early Earth’s atmosphere by mixing the gases in a flask and adding an electrical charge (simulate lightening)

10. 17.1 How Did Life Begin Urey-Miller Experimental Apparatus • Simple organic molecules appeared in just a few days • Small molecules likely present in early atmosphere can combine to form large organic molecules (nucleic acids, amino acids, proteins, lipids) if electrical energy is present

11. 17.1 How Did Life Begin Miller-Urey Experiment An electric spark simulates a lightning storm electric spark chamber Energy from the spark powers reactions among molecules thought to be present in Earth’s early atmosphere CH4 NH3 H2 H2O Boiling water adds water vapor to the artificial atmosphere When the hot gases in the spark chamber are cooled, water vapor condenses and any soluble molecules present are dissolved cool water flow condenser boiling chamber water Organic molecules appear after a few days

12. 17.1 How Did Life Begin • Modern geochemists believe early atmosphere was slightly different from that modeled in Miller and Urey’s experiments • Additional experiments with more realistic (but still oxygen-free) simulated atmospheres have also yielded organic molecules • Electricity not the only suitable energy source (heat and UV light)

13. 17.1 How Did Life Begin • Prebiotic synthesis neither efficient nor fast • prebiotic molecules threatened by sun’s UV radiation since Earth lacked an ozone layer • Ozone layer is a region high in today’s atmosphere made up of ozone molecules • (O3 – formed when solar energy splits O2 molecules • into individual O atoms which then react with other • O2 molecules)

14. Ozone Formation

15. Ozone layer • UV radiation can • provide energy for • formation of organic • molecules but can also • break them apart • organic molecules may • have accumulated under • rock ledges or bottoms of shallow seas away from UV radiation

16. 17.1 How Did Life Begin • RNA may have been the first self-reproducing molecule • DNA was probably not the earliest informational molecule • DNA requires large complex protein enzymes • Instructions for building these enzymes are coded in DNA http://www.sciencechannel.com/tv-shows/through-the-wormhole/videos/through-the-wormhole-from-rna-to-dna.htm

17. 17.1 How Did Life Begin • RNA can act as a catalyst (speeds rxns) • Thomas Cech and Sidney Altman (1980s) discovered a cellular reaction that was catalyzed by a protein, a small RNA molecule and coined the term ribozyme • Dozens of natural occurring ribozymes have been discovered since; found to catalyze reactions including attaching amino acids to growing proteins

18. 17.1 How Did Life Begin • Ribozyme discovery led to hypothesis that RNA preceded origin of DNA • first ribozyme continued to evolve and gradually developed into is present role as intermediary between DNA and protein synthesis

19. 17.1 How Did Life Begin • Self-replicating molecules on their own DON’T constitute life • membrane-like vesicles may have enclosed ribozymes • Protocells– spherical collection of proteins & lipids containing ribozymes (stepping stone to 1st cells)

20. 17.2 What Were the Earliest Organisms Like? • Earth formed 4.5 b.y.a and was HOT • Meteorites smashed into forming planet; kinetic energy converted into heat on impact • Geologic evidence suggests Earth cooled enough for water to exist in liquid form 4.3 b.y.a. • Oldest fossil organisms found (so far) are approximately 3.4 b.y.o • Life arose 3.9 b.y.a. in Precambrian era

21. How Do We Know How Old a Fossil Is? 17-1 http://education-portal.com/academy/lesson/the-history-of-life-on-earth-timeline-and-characteristics-of-major-eras.html#lesson (cuts off after a while) • Relative Dating (before 20th century) • Law of Superposition - Fossils in deeper rock layers were older than fossils found in shallower rock layers • Absolute Dating (1896) a. Radiometric dating – when the nuclei of radioactive elements spontaneously break down, or decay, into other elements b. Each radioactive element decays at a different rates

22. How Do We Know How Old a Fossil Is? 17-1 • Radiometric dating (cont.) a. Time it takes for half of a radioactive element’s (isotope) nuclei to decay at a specific rate is called half-life. b. Half-life of Carbon-14 = 5,730 years Half-life of Potassium-40 = 1.25 billion years c. Can estimate how much time has passed by measuring the proportion of decayed nuclei to undecayednulcei

23. Half-lives 256 14C atoms at time 0 128 14C and 128 14N atoms after 5,730 years or 1 half-life

24. 64 14C and 192 14N atoms after 11,460 years or 2 half-lives Half-lives 32 14C and 224 14N atoms after 17,190 years or 3 half-lives

25. Half-lives 16 14C and 240 14N atoms after 22,920 years or 4 half-lives 8 14C and 248 14N atoms after 28,650 years or 5 half-lives

26. Half-lives 4 14C and 252 14N atoms after 34,380 years or 6 half-lives 2 14C and 254 14N atoms after 40,110 years or 7 half-lives

27. 1 Proportion of isotope left 1/2 1/4 1/8 1/16 0 3 2 4 5 1 Half-lives Proportion of Isotope Left vs. Half Lives

28. How Do We Know How Old a Fossil Is? 17-1 • Hyphen notation of radioisotopes (element symbol and mass number) Examples: C-12, C-14, O-16, O-18 • Carbon-14 dating – compare ratio of C-14 and C-12 and use the ratio to determine age ISOTOPE Carbon-14 Uranium-235 Potassium-40 Uranium-238 HALF LIFE (years) 5,730 704,000,000 1,250,000,000 4,500,000,000

29. How Do We Know How Old a Fossil Is? 17-1 Sample Problem 1: The half-life of Thorium-230 is 75,000 years. If a scientist has 40.0g of Thorium, how much will remain after 225,000 years? ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ How many half-lives have past? How much Thorium is left? 225-75 = 150 150-75 = 75 40/2 = 20g 75-75 = 0 20/2 = 10g 3 half-lives have past 10/2 = 5g 5g of Thorium remaining after 225,000 years

30. The half life of carbon-14 is 5,730 years. How long will it take for ½ of the sample to decay? 1 half-life = 5,370years = ½ the sample decays • If a biologist has 64.0g of C-14, how long will it take until 8.0g remain un-decayed? 64/2 = 32g 1 half-life 5,730 x 3 half-lives = 32/2 = 16g 1 half-life 17, 190 years 16/2 = 8g 1 half-life 3 half-lives

31. 17.2 What Were the Earliest Organisms Like? The first organisms were anaerobic (don’t require oxygen to metabolize nutrients) prokaryotes (lack membrane bound nucleus) - Obtained nutrients & energy by absorbing organic molecules from their environment (heterotroph hypothesis)

32. 17.2 What Were the Earliest Organisms Like? • Some organisms evolved ability to capture sun’s energy when organic molecules were used up (photosynthetic bacteria) • Photosynthetic organisms release oxygen • Oxygen reacted with iron within Earth’s crust to form iron oxide (rust) which is why rocks formed during that time contain lots of iron

33. 17.2 What Were the Earliest Organisms Like? • Excess oxygen began accumulating in atmosphere (approx. 2.3 b.y.a) probably produced by bacteria like cyanobacteria • Very likely we are breathing some of the recycled oxygen expelled more than 2 b.y.a!!!!

34. 17.2 What Were the Earliest Organisms Like? • Aerobic metabolism arose in response to dangers posed by oxygen • Oxygen can react with organic molecules breaking them down • Oxygen may have exterminated many anaerobic organisms (natural selection) • Evolution of aerobic metabolism was significant because aerobic organisms can harvest more energy per food molecule than anaerobic organisms

35. 17.2 What Were the Earliest Organisms Like? • Some organisms acquired membrane-enclosed organelles • Ability to compartmentalize functions inside the cell improved efficiency of early cells • First • eukaryotes • (membrane- • bound • organelles) • appeared 1.7 • b.y.a.

36. 17.2 What Were the Earliest Organisms Like? • Mitochondria and chloroplasts may have arise from engulfed bacteria • Endosymbiosis hypothesis proposes that early eukaryotic cells acquired precursors of mitochondria and chloroplasts by engulfing certain types of bacteria

37. aerobic bacterium • Endosymbiosis • Hypothesis • Evidence? Many distinctive biochemical features shared by eukaryotic organisms and living bacteria An anaerobic, predatory prokaryotic cell engulfs an aerobic bacterium Descendants of the engulfed bacterium evolve into mitochondria photosynthetic bacterium The mitochondria- containing cell engulfs a photosynthetic bacterium Descendants of the photosynthetic bacterium evolve into chloroplasts https://www.youtube.com/watch?v=bBjD4A7R2xU

38. 17.2 What Were the Earliest Organisms Like? D-Anaerobic, prokaryotic, heterotrophs evolve from protocells (heterotroph hypothesis) B- Evolution of autrophic pathways chemosynthesis/photosynthesis H-Anaerobic, prokaryotic, autotrophs evolve (cyanobacteria) E-Oxygen released by photosynthesizers I- Aerobic prokaryotes evolve C- Endosymbiosis of aerobic prokaryotes (mitochondria) into anaerobic autotrophic prokaryotes G-Endosymbiosis of autotrophic prokaryotes (chloroplasts) into aerobic prokaryotes A-Evolution of eukaryotes F-Evolution of multicellular organisms

39. Review the following: • Ch. 1: Introduction to Life on Earth • Read Ch. 1 summary of key concepts on pg. 16 • Chapter 1 Vocab • --------------------Ch. 17-1 and 17-2: History of Life-------------------- • 1. Read Ch. 17-1 and 17-2 summary of key concepts on pg. 334 • 2. Chapter 17-1 and 17-2 Vocab