Chapter 20

Chapter 20 - Note that the following lectures include...

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Note that the following lectures include animations and PowerPoint effects such as fly ins and transitions that require you to be in PowerPoint's Slide Show mode (presentation mode).
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Planet Earth Chapter 20
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Astronomy has been described as the science of everything above the clouds. Planetary astronomers, however, must also think about what lies below the clouds because Earth is the basis for comparison with all other Earthlike planets. We know Earth well, and we can apply what we know about Earth to other worlds. There is another reason for studying Earth in an astronomy course. Astronomy is really about us. Astronomy is exciting and fascinating because it helps us understand what we are and where we are in the universe. Thus, we cannot omit Earth from our discussion—it is where we are. The next two chapters will discuss the Earthlike planets, but that will not end our thoughts of Earth. The moons of Guidepost
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the giant outer worlds will seem Earthlike in strange ways, and our discussion of the smaller bodies of our solar system will alert us to the dangers Earth faces. Throughout the rest of this book, we will remain painfully aware of the fragile beauty of our planet. Guidepost (continued)
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I. The Early History of Earth A. Four Stages of Planetary Development B. Earth as a Planet II. The Solid Earth A. Earth's Interior B. The Magnetic Field C. Earth's Active Crust III. The Atmosphere A. Origin of the Atmosphere B. Human Effects on Earth's Atmosphere Outline
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The Early History of Earth Earth formed 4.6 billion years ago from the inner solar nebula. Four main stages of evolution: Most traces of bombardment (impact craters) now destroyed by later geological activity Two sources of heat in Earth’s interior: Potential energy of infalling material Decay of radioactive material
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Earth’s Interior Direct exploration of Earth’s interior (e.g. drilling) is impossible. Earth’s interior can be explored through seismology: earthquakes produce seismic waves . Two types of seismic waves: P ressure waves: Particles vibrate back and forth S hear waves: Particles vibrate up and down
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Seismology Seismic waves do not travel through Earth in straight lines or at constant speed. They are bent by or bounce off transitions between different materials or different densities or temperatures. Such information can be analyzed to infer the structure of Earth’s interior.
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Seismic Waves (SLIDESHOW MODE ONLY)
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Earth’s Interior (2) Basic structure: Solid crust Solid mantle Liquid core Solid inner core Earth’s interior gets hotter towards the center. Earth’s core is as hot as the sun’s surface; metals are liquid. Melting point = temperature at which an element melts (transition from solid to liquid) Melting point increases with increasing pressure towards the center => Inner core becomes solid
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Earth’s Magnetic Field Convective motions and rotation of the core generate a dipole magnetic field Earth’s core consists mostly of iron + nickel: high electrical conductivity
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Chapter 20 - Note that the following lectures include...

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