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 lightning storms Mixture of gases simulating atmosphere of early Earth 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 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

Corrected Experiments Have Produced Cytosine & Uracil Original Atmospheric Components Not Accurate (Re-Analysis of Chemical Composition of Early Rocks) Corrected Experiments Have Produced Cytosine & Uracil Two RNA Bases

Copyright Pearson Prentice Hall 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 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-plant like protists Ancient Anaerobic Prokaryote Primitive Aerobic Eukaryote 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

Microfossils - 3.5 Billion Years Old 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

First It Bound Iron In The Oceans 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

Next O2 Accumulated In The Atmosphere Free Oxygen Next O2 Accumulated In The Atmosphere O2 Increased Methane & Hydrogen Sulfide Decreased Atmosphere Turned Blue

First Aerobic Organisms Arise 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