Origins of Life on Earth

1. Origins of Life on Earth Where did life come from?

2. Early Ideas Spontaneous Generation • Believed life “arose” from nonliving objects. • Mice came from piles of grain • Bees were produced from carcasses of cattle • Maggots came from rotting meat • Lice from sweat

3. Francesco Redi 1668 • Hypothesized maggots arose from eggs that were to small to see with the naked eye. • Tested his hypothesis by placing meat in several jars. • ½ open to air directly • ½ covered with gauze • Gauze covered were exposed to air • Maggots formed in open jars • No maggots formed in gauze covered jars • DISPROVED SPONTANEOUS GENERATION!!!

4. Francesco Redi

5. Francesco Redi A B C

6. John Needham • Attacked Redi’s conclusions • Sealed gravy in a bottle • Heated the bottle to kill the living organisms in it. • After several days, examined the bottle under a microscope • Found it swarming with microscopic organisms • Concluded the microorganisms “could only have come from the juice of the gravy.”

7. Lazzaro Spallanzani • Considered “Spontaneous Generation” • Knew of Redi’s & Needham’s experiments • Believed Needham was wrong. • Thought Needham didn’t kill bacteria by heating.

8. Lazzaro Spallanzani • Prepared identical gravy to Needham • Put ½ the gravy into one jar, the other ½ into another jar • Boiled both jars • Sealed one, left the other open to the air • After a few days, the open one was teeming with life • The sealed jar had no living things in it.

9. Lazzaro Spallanzani • Spallanzani concluded that the microorganisms did not come from the gravy, but entered the jar through the air (Air was a Vital Force). • People still believed that Spallanzani’s work was flawed. • They said that air was necessary for spontaneous generation. • By sealing the jar, the air was kept out.

10. Louis Pasteur • Finally disproved “Spontaneous Generation” • Placed nutrient broth similar to Needham and Spallanzani into some flasks with long curving necks • Boiled the flasks thoroughly • Waited for one year 1864

12. Louis Pasteur

13. Louis Pasteur • No microorganisms formed – even though open to the air • After a year, he broke the neck of some of the flasks • All developed microorganisms • Conclusion: Life from Life

14. Where did life come from? That’s the million dollar question

15. Early Ideas First atmosphere contained • Water vapor (H2O) • Carbon Monoxide (CO) • Nitrogen (N2) • Hydrogen Sulfide (H2S) • Hydrogen Cyanide (HCN) • No free oxygen • Could not support life as we know it • Geological evidence supports this because rocks from this period contain no iron oxide (Rust) or other compounds that require free oxygen to form

16. The Molecules of Life • Stanley Miller and Harold Urey • Miller recreated what he thought might have been earth’s earliest atmospheres by mixing -ammonia -water -hydrogen • in a flask & exposed the flask to electric sparks (Lightning)

17. Miller-Urey

18. Organic Soup? • In a few days, “Organic Soup” – complex molecules - urea - acetic acid - lactic acid - several amino acids - ATP - Nitrogenous base adenine

19. Complex Molecules of Life Formation of Complex Molecules • Russian Alexander Oparin and American Sidney Fox showed that the organic soup that formed in the oceans could form other compounds • In the absence of Oxygen, amino acids tend to link together to form chains.

20. What do chains of amino acids form? • Proteins

21. Protolife • Others compounds form carbohydrates, alcohols, and lipids • Collections of molecules like this tend to gather into round droplets • Some of these droplets grow and even reproduce • Some break down glucose • These droplets are called “proto-life” because they are not “alive”, but have begun to perform tasks necessary for life

22. Protolife to Cells • DNA & RNA must have somehow been created molecules can replicate

23. First Cells • Several hypotheses • Some believe first cells came from a shallow pool containing organic soup • when the organic soup is dried, lipids form spheres around small DNA molecules • Given time, a form of DNA that is capable of replicating could have arisen

24. First Cells • G. Cairns-Smith and J. Bernal: • noted attractive forces concentrate amino acids, DNA and RNA onto clay crystals • Held together, these may have formed lengths of proteins and DNA

25. First Cells • Several scientists believe the first cells formed near volcanic vents deep in the ocean • Very high temperatures • Lots of sulfur compounds • Assortment of chemicals • Strong currents to mix them • Deposits of clay

26. First Cells • scientists who duplicated these conditions observed the spontaneous synthesis of amino acids and RNA • First True Cells • First cells were prokaryotes • Resembled some bacteria • Heterotrophs • Anaerobes (can live without oxygen)

27. Photosynthesis • Heterotrophic cells could have survived for a long time without difficulty finding “Food” • Sooner or later, the food would run out. Complex molecules in the organic soup would be depleted. • Some organisms would have to develop complex molecules from simple ones • Natural selection would favor ability to harness outside energy source

28. Stromatolites • First cells probably used Hydrogen Sulfide instead of Water • Successful, spread rapidly and common 3.4 million years ago • Grew in mats called Stromatolites • Still can find stromatolites in special habitats, but fossils have been found all over the world

29. Stromatolites

30. Life from Non-life • We said that life did not come from non-life, how did life start?

31. Earth then … and now • Earth of today is very different from earth of billions of years ago. • No oxygen to break down organic compounds • Today, such compounds cannot remain intact in the natural world long enough to give another start to life • Road to Modern Organisms • 2.2 billion years ago, a more modern form of photosynthesis evolved. • The use of H2O instead of H2S

32. Deadly gas? • This put out deadly gas … • OXYGEN!

33. Effects of photosynthesis • Over the next 500 Million years, the waste product given off by some organisms changed the earth from an anaerobic planet to an aerobic planet. • Nearly 1/5 Oxygen

34. Oxygen • Because oxygen was toxic to anaerobes, they had to survive in areas with no oxygen such as deep in mud, or other places oxygen does not reach. • Oxygen was beneficial to those that survived • Oxygen that reached the upper atmosphere was changed from O2 to O3 (Ozone) that shielded earth from much of the UV light from the sun.

35. Aerobic Metabolism • Evolution of Aerobic Metabolism • organisms evolved that used Oxygen in their metabolic pathways (remember chapter 6) • 18X more efficient than anaerobic respiration

36. Eukaryotes • Eukaryotic cells • between 1.4 and 1.6 billion years ago, the first eukaryotic cells evolved.

37. Endosymbiont Hypothesis • Endosymbiont Hypothesis • Lynn Margulis • Noticed Chloroplasts and Mitochondria both had their own DNA • Circular piece of DNA similar to bacterial plasmid • Hypothesized that organelles were originally prokaryotes that somehow ended up inside another cell

38. Reproduction • Sexual reproduction • Sexual reproduction was an extremely large step towards evolution • Asexual reproduction makes exact copies of cells. Only chance of change is by mutation. • Sexual reproduction shuffles genetic material every time. • offspring never are exactly like parents

39. Multicellular • A few hundred million years after evolution of sexual reproduction – multicellular life • Great adaptive radiation • Life was on its way.