Foothill High School Science Department The History of Life Earth’s Early History

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Foothill High School Science Department Formation of Earth Key Concept Earth’s Early Atmosphere Contained: Hydrogen Cyanide Carbon Monoxide Hydrogen Sulfide Hydrogen Cyanide Carbon Dioxide Carbon Monoxide Nitrogen Hydrogen Sulfide Water

Foothill High School Science Department Formation of Earth The Material Forming Earth Probably Condensed From Stellar Debris Over 100 Million Years Surface Originally Molten Atmosphere Pinkish-Orange &

Foothill High School Science Department Condensation of Debris

Foothill High School Science Department Earth’s Early Atmosphere

Foothill High School Science Department 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

Foothill High School Science Department Early Crust Forms

Foothill High School Science Department Formation of Earth ~3.8 Billion Years Ago Earth Cooled Enough For Water To Condense Oceans Formed Green/Brown With Iron Thunderstorms Continuous Life Appeared

Foothill High School Science Department The First Organic Molecules Atoms Do Not Assemble Into Complex Organic Molecules Today Due To: Oxygen Oxygen is VERY Reactive & Bacteria Bacteria would eat them

Foothill High School Science Department Miller & Urey Stanley Miller & Harold Urey 1950’s - Chemists Simulated Earths Early Atmosphere In The Laboratory Ran Electric Sparks Through It Simulating Lightning

Foothill High School Science Department Miller & Urey Experiment Generated Amino Acids In Just A Few Days

Foothill High School Science Department 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.

Foothill High School Science Department Modified Miller & Urey Original Atmospheric Components Not Accurate Original Atmospheric Components Not Accurate (Re-Analysis of Chemical Composition of Early Rocks) Corrected Experiments Have Produced Cytosine & Uracil Two RNA Bases

Foothill High School Science Department How Did Life Begin? How Did Life Form From The Organic Soup Of Original Earth? Prokaryote Fossils These Fossils Date To Million Years After The Earth Cooled Enough For Water To Form

Foothill High School Science Department Formation of Microspheres Proteinoid Microspheres Proteinoid Microspheres – Large Organic Molecules Naturally Form Tiny Bubbles – Not Cells But Have Some Characteristics Of Living Systems e.g. Selective Permeable Membranes e.g. Selective Permeable Membranes

Foothill High School Science Department Evolution of RNA & DNA Still Unknown However: Still Unknown However: – RNA Sequences Have Been Found That: Help DNA Replicate Help DNA Replicate Transcribe DNA Transcribe DNA Translate Proteins Translate Proteins Catalyze Chemical Reactions Catalyze Chemical Reactions Duplicate Themselves Duplicate Themselves – Perhaps RNA Came First

Foothill High School Science Department Free Oxygen Microfossils Billion Years Old – Prokaryotes – Anaerobic (No O 2 In Atmosphere) – Photosynthetic Bacteria Arose 2.2 Billion Years Ago 2.2 Billion Years Ago O 2 Continuously Released Into The Atmosphere O 2 Continuously Released Into The Atmosphere

Foothill High School Science Department 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 Formed Great Bands Of Iron That We Mine Today Oceans Changed Turned Blue Oceans Changed Turned Blue

Foothill High School Science Department Free Oxygen Next O 2 Accumulated In The Atmosphere – O 2 Increased – Methane & Hydrogen Sulfide Decreased – Atmosphere Turned Blue

Foothill High School Science Department Free Oxygen Is Highly Reactive Deadly To Anaerobes First Aerobic Organisms Arise

Foothill High School Science Department 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

Foothill High School Science Department Variations in CO 2 and O 2

Foothill High School Science Department Variations in CO 2 and O 2 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

Foothill High School Science Department Origin of Eukaryotic Cells Began About 2 Billion Years Ago Began About 2 Billion Years Ago – Some Prokaryotes Started Developing Inner Cell Membranes

Foothill High School Science Department Origin of Eukaryotic Cells Endosymbiotic Theory Endosymbiotic Theory – Some Smaller Prokaryotes Began Living In Larger Prokaryotes. A Symbiotic Relationship Developed Some Became Mitochondria Some Became Mitochondria Some Became Chloroplasts Some Became Chloroplasts

Foothill High School Science Department 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

Foothill High School Science Department Origin of Eukaryotic Cells Lynn Margulis – Boston U. 1960’s Lynn Margulis – Boston U. 1960’s – Evidence Mitochondria & Chloroplasts Contain DNA & Ribosomes Similar To Bacterial DNA & Ribosomes Mitochondria & Chloroplasts Contain DNA & Ribosomes Similar To Bacterial DNA & Ribosomes – They Reproduce By Binary Fission

Foothill High School Science Department Sexual Reproduction & Multicellularity Shortly After Forming Multicellular Organisms Sexual Reproduction Began Shortly After Forming Multicellular Organisms Sexual Reproduction Began – Accelerated Development of Genetic Variation – A Few Hundred Million Years Later, Multicellular Organisms Arose And Exploded

Foothill High School Science Department