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Understanding Earth's Formation: The Nebular Hypothesis and Unique Features of Our Planet

This lecture explores the Nebular Hypothesis, detailing how planets formed from a disk of gas and dust. We delve into the early atmosphere of Earth, which was primarily composed of hydrogen and helium, and how volcanic outgassing contributed to the current atmosphere, rich in nitrogen and oxygen. Discussion includes significant changes in atmospheric composition, evolutionary milestones such as the emergence of cyanobacteria, and the impact of geological time on understanding Earth's history. Fundamental theories are also reviewed, including catastrophism and uniformitarianism.

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Understanding Earth's Formation: The Nebular Hypothesis and Unique Features of Our Planet

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  1. The Earth in Context GLY 2010 – Summer 2013 Lecture 2

  2. Nebular Hypothesis

  3. Painting of Nebula • An artistic impression of the nebula disk of gas and dust from which the planets in our solar system grew • Image: Don Dixon

  4. Collisions Between Planetesimals • Don Dixon’s impression of collisions between planetesimals – a gravitationally driven mechanism for accretion of the planetary embryos that eventually built the Earth

  5. The Earth In Context

  6. Unique Features of the Earth • Liquid water oceans • Free oxygen in the atmosphere

  7. The Earth Is a Differentiated Planet - It Has Layers

  8. Early Atmosphere • Earth’s original atmosphere - Hydrogen and Helium • Light elements escape • Earth’s current atmosphere is secondary and evolved from other processes

  9. Outgassing • Early volcanism emitted gases into the atmosphere • Present day volcanic gas composition • Water Vapor ~ 50--60% • Carbon Dioxide ~ 24% • Sulfur ~ 13% • Nitrogen ~ 5.7% • Argon ~ 0.3%

  10. Earth’s Atmosphere Today • Nitrogen ~ 78% • Oxygen ~ 21% • Argon ~ 1% • Carbon dioxide ~ 396.78 parts per million (0.039%), measured at Mauna Loa, Hawaii in May, 2012 • Increased from 394.16 in May, 2011

  11. Problems • Not enough water to fill oceans • No oxygen in the atmosphere • Carbon dioxide levels much too high • Sulfur gas levels much too high

  12. Changes • Carbon dioxide and sulfur gases are absorbed by water and removed in rain • Resulting acid solutions weather the rocks • Carbon dioxide becomes limestone • Sulfur gases become sulfide minerals

  13. Oxygen? • The early earth had no oxygen • Life appeared on earth at least 3.5 billion years ago – recent claims of 3.9 billion, and perhaps even 4.4 billion • Cyanobacteria appeared around 2.5 billion years ago

  14. Catastrophism • Early theory – series of catastrophes • Earthquakes • Volcanic eruptions • Floods • Age of earth assumed to be a few thousand years Abraham Gottlob Werner, 1750-1817

  15. James Hutton, 1726-1797 • Originator “The present is the key to the past” • Originator of the concept of “deep time”

  16. Uniformitarianism

  17. Geologic Time

  18. Paleozoic Era • Trilobite fossil, early Paleozoic era

  19. Mesozoic Era • Dinosaurs were the dominant life forms

  20. Cenozoic Era • Kangaroos are marsupials, a type of mammal

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