Outline 17-2: Earth's Early History Photo credit: Jackie Beckett/American Museum of Natural History Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall I. Early Earth A. The Earth is thought to be 4.5 - 5 billion years old. 1. At first a fiery ball of molten rock 2. Eventually cooled & formed a rocky crust 3. Water vapor condensed to form oceans a. Scientists think that first life evolved in these oceans Copyright Pearson Prentice Hall

II. Origins of Living Cells A. Biogenesis does not answer the question: 1. How did life begin on Earth? a. No one will ever know for certain how life began b. Scientists have developed theories about the origin of life from testing scientific hypotheses about conditions on early Earth Copyright Pearson Prentice Hall

B. How basic chemicals could form 1. All elements necessary for life were apparently found on Earth from its beginnings. a. Physical & chemical processes alone can explain the origins of ever more complex organic chemicals on our planet b. This hypothesis has been tested & confirmed many times in laboratory experiments. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 2. Primordial soup model a. Oparin & Haldane’s (1920s) idea:  Earth’s early atmosphere contained ammonia, hydrogen, methane & water vapor  Heat from volcanoes, sunlight and lightning could have caused them to form organic compounds  Accumulated in a sea called the primordial soup Copyright Pearson Prentice Hall

3. Miller & Urey’s Experiment (1953) a. Tested Oparin’s hypothesis  Put suggested gases in chamber  Used sparks to simulate lightning b. Results:  Complex chemical “zoo” which included organic compounds like : amino acids fatty acids hydrocarbons Copyright Pearson Prentice Hall

The First Organic Molecules Miller and Urey’s Experiment Mixture of gases simulating atmosphere of early Earth Spark simulating lightning storms Condensation chamber Water vapor Cold water cools chamber, causing droplets to form. Miller and Urey produced amino acids, which are needed to make proteins, by passing sparks through a mixture of hydrogen, methane, ammonia, and water. This and other experiments suggested how simple compounds found on the early Earth could have combined to form the organic compounds needed for life. Liquid containing amino acids and other organic compounds Copyright Pearson Prentice Hall

4. Reevaluating primordial soup model a. Early atmosphere probably did NOT contain methane & ammonia. It probably contained hydrogen cyanide, carbon dioxide, carbon monoxide, nitrogen, hydrogen sulfide, and water. b. Without methane & ammonia some key biological molecules are not made. c. So how could organic molecules form? Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 5. Bubble model a. Louis Lerman (1986) suggested key processes took place within bubbles on the ocean’s surface.  While inside bubbles, gases get protection from UV radiation  Reactions could take place faster inside bubbles (concentrated)  Bubbles could later rise to surface & release organic molecules into ocean  Energy could cause these to react & build even more complex molecules Copyright Pearson Prentice Hall

C. How complex chemicals could form 1. Amino acids could have then spontaneously linked together to form proteins 2. RNA has been found to form spontaneously in water a. RNA could have been first self- replicating molecule b. It could also have catalyzed the first assembly line of proteins Copyright Pearson Prentice Hall

The Puzzle of Life's Origin Proteins build cell structures and catalyze chemical reactions RNA and the Origin of Life RNA nucleotides Simple organic molecules RNA helps in protein synthesis Abiotic “stew” of inorganic matter One hypothesis about the origin of life, illustrated here, suggests that RNA could have evolved before DNA. Scientists have not yet demonstrated the later stages of this process in a laboratory setting.  RNA able to replicate itself, synthesize proteins, and function in information storage DNA functions in information storage and retrieval Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 3. Microspheres Cells a. Lipids have been shown to gather in water & form a bilayer sphere b. Chains of amino acids will gather into tiny vesicles called proteinoid microspheres c. Have selectively permeable membranes & can store & release energy d. These vesicles could have been first step toward cells Problem: They don’t reproduce! Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Free Oxygen III. Oldest Fossils A. Are microfossils of unicellular prokaryotic organisms resembling modern bacteria B. Found in rocks 3.5 billion years old. C. Were anaerobic organisms. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Free Oxygen IV. First Oxygen A. About 2.2 billion years ago, photosynthetic bacteria began to pump oxygen into the oceans. B. Next, oxygen gas accumulated in the atmosphere. C. Rise of oxygen probably caused some life forms to go extinct while others took advantage of oxygen in new ways (aerobic respiration) Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Free Oxygen V. The Endosymbiotic Theory A. Idea that eukaryotic cells formed from a symbiosis among several different prokaryotes. 1. Ones that used oxygen evolved into mitochondria 2. Ones that could do photosynthesis evolved into chloroplasts Copyright Pearson Prentice Hall

Origin of Eukaryotic Cells DON’T COPY! Endosymbiotic Theory Ancient Prokaryotes Chloroplast Plants and plantlike protists Aerobic bacteria Photosynthetic bacteria Nuclear envelope evolving Mitochondrion Primitive Photosynthetic Eukaryote The endosymbiotic theory proposes that eukaryotic cells arose from living communities formed by prokaryotic organisms. Ancient prokaryotes may have entered primitive eukaryotic cells and remained there as organelles. Animals, fungi, and non-plantlike protists Ancient Anaerobic Prokaryote Primitive Aerobic Eukaryote Copyright Pearson Prentice Hall

Origin of Eukaryotic Cells DON’T COPY! Aerobic bacteria Ancient Prokaryotes Nuclear envelope evolving The endosymbiotic theory proposes that eukaryotic cells arose from living communities formed by prokaryotic organisms. Ancient prokaryotes may have entered primitive eukaryotic cells and remained there as organelles. Ancient Anaerobic Prokaryote Copyright Pearson Prentice Hall

Origin of Eukaryotic Cells DON’T COPY! Mitochondrion Prokaryotes that use oxygen to generate energy-rich molecules of ATP evolved into mitochondria. The endosymbiotic theory proposes that eukaryotic cells arose from living communities formed by prokaryotic organisms. Ancient prokaryotes may have entered primitive eukaryotic cells and remained there as organelles. Primitive Aerobic Eukaryote Copyright Pearson Prentice Hall

Origin of Eukaryotic Cells DON’T COPY! Prokaryotes that carried out photosynthesis evolved into chloroplasts. Chloroplast Photosynthetic bacteria The endosymbiotic theory proposes that eukaryotic cells arose from living communities formed by prokaryotic organisms. Ancient prokaryotes may have entered primitive eukaryotic cells and remained there as organelles. Primitive Photosynthetic Eukaryote Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 17-2 Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 17-2 Which of the following gases was probably NOT present in the early Earth’s atmosphere? hydrogen cyanide oxygen nitrogen carbon monoxide Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 17-2 Miller and Urey's experiment was a simulation of Earth's early volcanic activity. formation. atmosphere. life. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 17-2 Proteinoid microspheres are different from cells because microspheres have selectively permeable membranes. do not have DNA or RNA. have a simple means of storing and releasing energy. separate their internal environment from the external environment. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 17-2 The hypothesis that RNA sequences appeared before DNA sequences has some evidence in its favor but is still being tested. has been rejected since DNA is required to make RNA. has been proven since RNA has been made in laboratories. has been rejected because it is illogical. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 17-2 As concentrations of oxygen rose in the ancient atmosphere of Earth, organisms began to evolve anaerobic pathways. plasma membranes. metabolic pathways that used oxygen. photosynthesis. Copyright Pearson Prentice Hall