1. Lesson Overview Lesson Overview Earth’s Early History Lesson Overview 19.3 Earth’s Early History

2. Lesson Overview Lesson Overview Earth’s Early History THINK ABOUT IT How did life on Earth begin? What were the earliest forms of life? How did life and the biosphere interact? Origin-of-life research is a dynamic field. But even though some current hypotheses will likely change, our understanding of other aspects of the story is growing.

3. Lesson Overview Lesson Overview Earth’s Early History The Mysteries of Life’s Origins What do scientists hypothesize about early Earth and the origin of life?

4. Lesson Overview Lesson Overview Earth’s Early History The Mysteries of Life’s Origins What do scientists hypothesize about early Earth and the origin of life? Earth’s early atmosphere contained little or no oxygen. It was principally composed of carbon dioxide, water vapor, and nitrogen, with lesser amounts of carbon monoxide, hydrogen sulfide, and hydrogen cyanide.Earth’s early atmosphere contained little or no oxygen

5. Lesson Overview Lesson Overview Earth’s Early History The Mysteries of Life’s Origins Pasteur 1880’s Louis Pasteur disproved spontaneous generation with a classic experiment with a curved bottled and chicken broth and hence any naturalistic origin of life.classic experiment Oparin (p553) 1920’s First to propose the Earth early atmosphere did’n t contain Oxygen.It was made mostly of Carbon dioxide, water vapor, nitogen, with lesser amount of hydrogen sulfide and hydrogen cyanide. He also proposed that biochemical Metabolism had to evolved before the first living cell appeared and that a source of energy was essential for that metabolism to happen. Oparin and Haldane coined the term “Primordial Soup” to the ancient oceans of early Earth. Miller and Urey’s ( p554)1953 experiment suggested a model showing how mixtures of the organic compounds necessary for life could have arisen from simpler compounds on a primitive Earth. Fox (p554) 1957 Sidney Walter Fox (24 March 1912 - 10 August 1998) biochemist.Based on Miller & Urey experiment he he proposed some hypothesis on the origins of life. Fox explored the synthesis of amino acids from inorganic molecules, the synthesis of proteinous amino acids and amino acid polymers called "proteinoids" from inorganic molecules and thermal energy, and created what he thought was the world's first spherical "protocells" out of proteinoids and water. He called these protocells "microspheres" and they have now been named "protobionts." Fox believed in spontaneous generation of life and suggested that his experiments possessed conditions that were similar to those of primordial Earth. In his experiments, he demonstrated that it is possible to create protein-like structures from inorganic molecules and thermal energy (abiogenesis)biochemist amino acidsproteinoidsmicrospheresprotobionts

6. Lesson Overview Lesson Overview Earth’s Early History The Mysteries of Life’s Origins Margulis (p557) 1960’s First to explain the origin of mitochondria and chloroplasts. She also proposed that eukaryotic flagella and cilia derived from endosymbiotic spirochetes.( cells unite with other cells to make a mutualistic relation) film on endosymbiosis (Video youtube)film on endosymbiosis What do scientists hypothesize about early Earth and the origin of life? “The RNA world” hypothesis proposes that RNA existed by itself before DNA. From this simple RNA-based system, several steps could have led to DNA-directed protein synthesis.

7. Lesson Overview Lesson Overview Earth’s Early History The Mysteries of Life’s Origins Geological and astronomical evidence suggests that Earth formed as pieces of cosmic debris collided with one another. While the planet was young, it was struck by one or more huge objects, and the entire globe melted.

8. Lesson Overview Lesson Overview Earth’s Early History The Mysteries of Life’s Origins For millions of years, violent volcanic activity shook Earth’s crust. Comets and asteroids bombarded its surface. About 4.2 billion years ago, Earth cooled enough to allow solid rocks to form and water to condense and fall as rain. Earth’s surface became stable enough for permanent oceans to form.

9. Lesson Overview Lesson Overview Earth’s Early History The Mysteries of Life’s Origins This infant planet was very different from Earth today. Earth’s early atmosphere contained little or no oxygen. It was principally composed of carbon dioxide, water vapor, and nitrogen, with lesser amounts of carbon monoxide, hydrogen sulfide, and hydrogen cyanide. Because of the gases in the atmosphere, the sky was probably pinkish- orange. Because they contained lots of dissolved iron, the oceans were probably brown.

10. Lesson Overview Lesson Overview Earth’s Early History The First Organic Molecules In 1953, chemists Stanley Miller and Harold Urey tried recreating conditions on early Earth to test the hypothesis that complexe organic molecules could have been formed from simpler inorganic atmospheric molecules such as CO2, N2 and H2O They filled a sterile flask with water, to simulate the ocean (“primordial soup”), and boiled it. Mille/Urey animation

11. Lesson Overview Lesson Overview Earth’s Early History The First Organic Molecules To the water vapor, they added methane, ammonia, and hydrogen, to simulate what they thought had been the composition of Earth’s early atmosphere. They passed the gases through electrodes, to simulate lightning.

12. Lesson Overview Lesson Overview Earth’s Early History The First Organic Molecules Next, they passed the gases through a condensation chamber, where cold water cooled them, causing drops to form. The liquid continued to circulate through the experimental apparatus for a week. After a week, they had produced 21 amino acids—building blocks of proteins.

13. Lesson Overview Lesson Overview Earth’s Early History The First Organic Molecules Miller and Urey’s experiment suggested how mixtures of the organic compounds necessary for life could have arisen from simpler compounds on a primitive Earth. We now know that Miller and Urey’s ideas on the composition of the early atmosphere were incorrect. But new experiments based on current ideas of the early atmosphere have produced similar results.

14. Lesson Overview Lesson Overview Earth’s Early History Formation of Proteinoid Microspheres (FOX) Geological evidence suggests that during the Archean Eon, 200 to 300 million years after Earth cooled enough to carry liquid water, cells similar to bacteria were common. How did these cells originate? Large organic molecules made of amino acids polymers under heat energy, form tiny bubbles called proteinoid microspheres under certain conditions. Microspheres are not cells, but they have some characteristics of living systems such as : selectively permeable through which water molecules and some gas can pass.

15. Lesson Overview Lesson Overview Earth’s Early History Formation of Microspheres Like cells, microspheres have selectively permeable membranes through which water molecules can pass. Microspheres also have a simple means of storing and releasing energy. Several hypotheses suggest that structures similar to proteinoid microspheres acquired the characteristics of living cells as early as 3.8 billion years ago.

16. Lesson Overview Lesson Overview Earth’s Early History Evolution of RNA and DNA Cells are controlled by information stored in DNA, which is transcribed into RNA and then translated into proteins. The “RNA world” hypothesis about the origin of life suggests that RNA evolved before DNA. From this simple RNA-based system, several steps could have led to DNA-directed protein synthesis.

17. Lesson Overview Lesson Overview Earth’s Early History Evolution of RNA and DNA A number of experiments that simulated conditions on early Earth suggest that small sequences of RNA could have formed from simpler molecules. Under the right conditions, some RNA sequences help DNA replicate. Other RNA sequences process messenger RNA after transcription. Still other RNA sequences catalyze chemical reactions. Some RNA molecules even grow and replicate on their own.

18. Lesson Overview Lesson Overview Earth’s Early History Evolution( by natural selection) of RNA and DNA One hypothesis about the origin of life suggests that RNA evolved before DNA. 1) RNA world Hypothesis Biochemical completion1) RNA world Hypothesis Biochemical completion Youtube Video 2) Orgin of Life with RNA

19. Lesson Overview Lesson Overview Earth’s Early History Production of Free Oxygen Microscopic fossils, or microfossils, of prokaryotes that resemble bacteria have been found in Archean rocks more than 3.5 billion years old. Those first life forms evolved in the absence of oxygen gas (O2) because at that time was rare. Oxygen atoms may be found in compound such as water (H2O) and carbon dioxide (Co2). Oxygen was present in Earth’s atmosphere in very little amout. It is formed in stars and the third-most abundant element in the universe ;hence, Oxygen gas could have been “imported” though crashing comets and meteorites like some of the water and carbon dioxide gas.abundant element

20. Lesson Overview Lesson Overview Earth’s Early History Production of Free Oxygen During the early Proterozoic Eon, photosynthetic bacteria became common. By 2.2 billion years ago, these organisms were producing oxygen.

21. Lesson Overview Lesson Overview Earth’s Early History Production of Free Oxygen At first, the oxygen combined with iron in the oceans, producing iron oxide, or rust. Iron oxide, which is not soluble in water, sank to the ocean floor and formed great bands of iron that are the source of most iron ore mined today. Without iron, the oceans changed color from brown to blue-green.

22. Lesson Overview Lesson Overview Earth’s Early History Production of Free Oxygen Next, oxygen gas began to accumulate in the atmosphereNext, oxygen gas began to accumulate in the atmosphere. (You tube video from cell to advanced multicellular organisms, Cambrian explosion etc… 10”) The ozone layer began to form, and the skies turned their present shade of blue. Over several hundred million years, oxygen concentrations rose until they reached today’s levels

23. Lesson Overview Lesson Overview Earth’s Early History Production of Free Oxygen Many scientists think that Earth’s early atmosphere may have been similar to the gases released by a volcano today. The graphs show the composition of the atmosphere today and the composition of gases released by a volcano.

24. Lesson Overview Lesson Overview Earth’s Early History Production of Free Oxygen To the first cells, which evolved in the absence of oxygen, this reactive oxygen gas was a deadly poison that drove this type of early life to extinction. Some organisms, however, evolved new metabolic pathways that used oxygen for respiration and also evolved ways to protect themselves from oxygen’s powerful reactive abilities.

25. Lesson Overview Lesson Overview Earth’s Early History Origin of Eukaryotic Cells What theory explains the origin of eukaryotic cells?

26. Lesson Overview Lesson Overview Earth’s Early History Origin of Eukaryotic Cells What theory explains the origin of eukaryotic cells? The endosymbiotic theory proposes that a symbiotic relationship evolved over time, between primitive eukaryotic cells and the prokaryotic cells within them.The endosymbiotic theory proposes

27. Lesson Overview Lesson Overview Earth’s Early History Origin of Eukaryotic Cells One of the most important events in the history of life was the evolution of eukaryotic cells from prokaryotic cells. Eukaryotic cells have nuclei, but prokaryotic cells do not. Eukaryotic cells also have complex organelles. Virtually all eukaryotes have mitochondria, and both plants and algae also have chloroplasts. 1.Endosymbiosis Animation

28. Lesson Overview Lesson Overview Earth’s Early History Endosymbiotic Theory It is believed that about 2 billion years ago, some ancient prokaryotes began evolving internal cell membranes. These prokaryotes were the ancestors of eukaryotic organisms. According to endosymbiotic theory, prokaryotic cells entered those ancestral eukaryotes. The small prokaryotes began living inside the larger cells.

29. Lesson Overview Lesson Overview Earth’s Early History Endosymbiotic Theory Over time a symbiotic relationship evolved between a community of 3 kind prokaryotic cells. 1.Small Ancient photosynthetic bacteria(prokaryote) 2.Small Ancient aerobic bacteria(prokaryote) 3.Larger Ancient Anaerobic prokaryote

30. Lesson Overview Lesson Overview Earth’s Early History Endosymbiotic Theory The endosymbiotic theory was proposed more than a century ago. At that time, microscopists saw that the membranes of mitochondria and chloroplasts resembled the cell membranes of free-living prokaryotes. This First observation led to two related hypotheses.

31. Lesson Overview Lesson Overview Earth’s Early History Endosymbiotic Theory 1) hypothesis proposes that mitochondria evolved from endosymbiotic prokaryotes that were able to metabolize oxygen to generate energy- rich ATP molecules. Without this ability to metabolize oxygen, cells would have been killed by the free oxygen in the atmosphere.

32. Lesson Overview Lesson Overview Earth’s Early History Endosymbiotic Theory The Second hypothesis proposes that chloroplasts evolved from endosymbiotic prokaryotes that had the ability to photosynthesize. Over time, these photosynthetic prokaryotes evolved within eukaryotic cells into the chloroplasts of plants and algae.

33. Lesson Overview Lesson Overview Earth’s Early History 5 Modern Evidences for Endosymbiosis hypothesis 1) During the 1960s, Lynn Margulis of Boston University noted that mitochondria and chloroplasts contain DNA similar to bacterial DNA. 2)She also noted that mitochondria and chloroplasts have ribosomes whose size and structure closely resemble those of bacteria. 3)In addition, she found that mitochondria and chloroplasts, like bacteria, reproduce by binary fission when cells containing them divide by mitosis. 4) mitochondria and chloroplasts had cell membrane like bacteria These similarities provide strong evidence of a common ancestry between free-living bacteria and the organelles of living eukaryotic cells. 5) mitochondria and chloroplasts are the same size as bacteria animation of Endosymbiosis

34. Lesson Overview Lesson Overview Earth’s Early History Sexual Reproduction and Multicellularity What is the evolutionary significance of sexual reproduction?

35. Lesson Overview Lesson Overview Earth’s Early History Sexual Reproduction and Multicellularity What is the evolutionary significance of sexual reproduction? The development of sexual reproduction sped up evolutionary change because sexual reproduction increases genetic variation.

36. Lesson Overview Lesson Overview Earth’s Early History Significance of Sexual Reproduction When prokaryotes reproduce asexually, they duplicate their genetic material and pass it on to daughter cells. This process is efficient, but it yields daughter cells whose genomes duplicate their parent’s genome. Genetic variation is basically restricted to mutations in DNA.

37. Lesson Overview Lesson Overview Earth’s Early History Summary 1)Oparin (1920’s) proposed that Metabolism appeared first, before life arose, using molecules from an anaerobic atmosphere. Simple inorganic molecules were transformed into complex bio- macromolecules using lighting as the source of energy. 2)Formation organic aggregate first and then of Proteonoid microsphere with selectively permeable membrane 3).”RNA world". From a lot of different models, Natural selection select the “fittest RNA”. RNA is a simpler molecule that later helped the more complex DNA to translate its genetic code into Proteins. RNA had to appear first. 4)4.B.Y.A DNA a product of RNA mutations. The earliest cells absorbed energy and food (heterotrophs)from the surrounding environment. They used fermentation, the breakdown of more complex compounds into less complex compounds with less energy, and used the energy so liberated to grow and reproduce. Fermentation can only occur in an anaerobic = anoxygenic (oxygen-free) environmentfermentation 5)3.8 B.Y.A Chemo-autotrophs (anoxygenic) appeared >Archaea using Hydrogen sulfide as a source of energy.DNA might have been present 6)2.2 B.Y.A Photoautotrophs prokaryotes> first appearance of Oxygen in the atmosphere, a byproduct of photosynthesis when H2o(Hydrogen Oxide) is split> future chloroplast 7)Heterotroph prokaryotes metabolize oxygen and the carbohydrate produced by the photo- autotrophs> future mitochondria 8)2. B.Y.A Endosymbiosis hypothesis : mitochondria & chloroplast appear 9)600 m. y. a :In the Ocean only. Simple Multicellular organism reproduction by mitosis 10) 550 m y. a :Appearance of collagen, advanced multicellular and sexual reproduction which bring about greater variation> adaptive radiation> “Cambrian explosion”