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Chapter 17 The History of Life. Section 17-2 Earth’s Early History. Picture Credits. Most Pictures In This PowerPoint Were Downloaded From:. Formation of Earth. Key Concept Earth’s Early Atmosphere Probably Contained:
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Chapter 17The History of Life Section 17-2Earth’s Early History
Picture Credits Most Pictures In This PowerPoint Were Downloaded From:
Formation of Earth Key Concept Earth’s Early Atmosphere Probably Contained: Hydrogen CyanideCarbon DioxideCarbon MonoxideNitrogenHydrogen SulfideWater
Formation of Earth The Material Forming Earth Probably Condensed From Stellar Debris Over 100 Million Years Surface Originally Molten Atmosphere Pinkish-Orange &
Formation of Earth ~4 Billion Years Ago Earth Cooled Enough For A Crust To Form Volcanic Activity Constant Comet & Asteroid Hits Constant Kept Earth Hot
Formation of Earth ~3.8 Billion Years Ago Earth Cooled Enough For Water To Condense Oceans Formed Brown With Iron Thunderstorms ContinuousLife Appeared
The First Organic Molecules Atoms Do Not Assemble Into Complex Organic Molecules Today Due To: Oxygen is VERY Reactive& Bacteria would eat them
Miller & Urey Stanley Miller & Harold Urey 1950’s Chemists Simulated Earths Early Atmosphere In The Laboratory Ran Electric Sparks Through It Simulating Lightning
Miller & Urey • Experiment Generated Amino Acids In Just A Few Days
Miller & Urey Key Concept Miller & Urey’s Experiments Suggested How Mixtures Of The Organic Compounds Necessary For Life Could Have Arisen From Simpler Compounds Present On A Primitive Earth.
Modified Miller & Urey Original Atmospheric Components Not Accurate Corrected Experiments Have Produced Cytosine & Uracil Two RNA Bases
How Did Life Begin? How Did Life Form From The Organic Soup Of Original Earth? Prokaryote Fossils Found. These Fossils Date To 200-300 Million Years After The Earth Cooled Enough For Water To Form
Formation of Microspheres • Proteinoid Microspheres • Large Organic Molecules Naturally Form Tiny Bubbles • Not Cells But Have Some Characteristics Of Living Systems • e.g. Selective Permeable Membranes
Evolution of RNA & DNA • Still Unknown However: • RNA Sequences Have Been Found That: • Help DNA Replicate • Transcribe DNA • Translate Proteins • Catalyze Chemical Reactions • Duplicate Themselves • Perhaps RNA Came First
Free Oxygen Microfossils - 3.5 Billion Years Old • Prokaryotes • Anaerobic (No O2 In Atmosphere) • Photosynthetic Bacteria Arose • 2.2 Billion Years Ago • O2 Continuously Released Into The Atmosphere
Free Oxygen First It Bound Iron In The Oceans • Iron Oxides Settled To The Bottom Of The Oceans • Formed Great Bands Of Iron That We Mine Today • Oceans Changed Turned Blue
Free Oxygen Next O2 Accumulated In The Atmosphere • O2 Increased • Methane & Hydrogen Sulfide Decreased • Atmosphere Turned Blue
Free Oxygen Is Highly Reactive Deadly To Anaerobes First Aerobic Organisms Arise
Free Oxygen Key Concept The Rise Of Oxygen In The Atmosphere Drove Some Life Forms To Extinction, While Other Life Forms Evolved New, More Efficient Metabolic Pathways That Used Oxygen For Respiration
Origin of Eukaryotic Cells • Began About 2 Billion Years Ago • Some Prokaryotes Started Developing Inner Cell Membranes
Origin of Eukaryotic Cells • Endosymbiotic Theory • Some Smaller Prokaryotes Began Living In Larger Prokaryotes. A Symbiotic Relationship Developed • Some Became Mitochondria • Some Became Chloroplasts
Origin of Eukaryotic Cells Key Concept: The Endosymbiotic Theory Proposes That Eukaryotic Cells Arose From Living Communities Of Prokaryotic Organisms First Proposed 100 Years Ago
Origin of Eukaryotic Cells • Lynn Margulis – Boston U. 1960’s • Evidence • Mitochondria & Chloroplasts Contain DNA & Ribosomes Similar To Bacterial DNA & Ribosomes • They Reproduce By Binary Fission
Sexual Reproduction & Multicellularity • Shortly After Forming Sexual Reproduction Began • Accelerated Development of Genetic Variation • A Few Hundred Million Years Later, Multicellular Organisms Arose And Exploded