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Download Chapter 17 Section 2 Earth’s Early History
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Chapter 17 Section 2 Earth’s Early History Objectives: -Describe how conditions on early Earth were different from conditions today -Explain what Miller and Urey’s experiments showed -State the hypotheses that have been proposed for how life first arose on Earth -Identify some of the main evolutionary steps in the early evolution of life Key Concept Earth’s Early Atmosphere Contained: Hydrogen Cyanide Carbon Dioxide Carbon Monoxide Nitrogen Hydrogen Sulfide Water The First Organic Molecules • Miller and Urey’s Experiment Spark simulating Mixture of gases simulating atmosphere of early Earth lightning storms Condensation chamber Water vapor Cold water cools chamber, causing droplets to form. Liquid containing amino acids and other organic compounds large organic molecules form tiny bubbles called proteinoid microspheres. Copyright Pearson Prentice Hall 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 Original Atmospheric Components Not Accurate (Re-Analysis of Chemical Composition of Early Rocks) Corrected Experiments Have Produced Cytosine & Uracil Two RNA Bases 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 • Endosymbiotic Theory Ancient Prokaryotes Chloroplast Aerobic bacteria Nuclear envelope evolving Ancient Anaerobic Prokaryote Photosynthetic bacteria Plants and plantlike protists Mitochondrion Primitive Aerobic Eukaryote Primitive Photosynthetic Eukaryote Animals, fungi, and non-plant like protists Copyright Pearson Prentice Hall 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 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 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 Variations in CO2 and O2 C = Cambrian O = Ordovician S = Silurian D = Devonian C = Carboniferous P = Permian Tr= Triassic J = Jurassic K = Cretaceous T = Tertiary “0” on time scale = Today Sexual Reproduction & Multicellularity • Shortly After Forming Multicellular Organisms Sexual Reproduction Began – A Few Hundred Million Years Later, Multicellular Organisms Arose And Exploded – Accelerated Genetic Variation
