Lecture16 - EAS 1600 Introduction to Environmental Sciences...

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EAS 1600 Introduction to Environmental Sciences ____________________________ Class 16 - Plate Tectonics: Part 2 A more detailed look at plate tectonic-processes _____________________________ In the last lecture we looked at the types of Plate motion and the development of Tectonics Theory. Today we will discuss: The forces that move the plates A comprehensive global view of Tectonics How our dynamic Earth works and how it has evolved. ENERGETICS OF PLATE TECTONICS Plates move an average of about 4 cm/yr. (Not very fast, you say, but how far would that amount to after 1 million years? Compare that distance to the circumference of the earth.) What is the energy source that drives this motion? < It comes from the earth’s interior - geothermal energy < Amounts to about 0.1 W/m 2 (How does this compare to solar input?) < The source of this energy is: 1. Radioactive decay; and 2. Residual heat from Earth’s formation 1. Radioactive decay - arises from the spontaneous decomposition of unstable isotopes of potassium, uranium, and thorium contained within the solid earth > For example, 40 K decays into 40 Ar with a half-life of 1.25 billion years When these elements decay they give off energy (like an atomic fission reaction). > All radioactive elements in earth’s interior are decreasing in abundance as they decay. Radioactive heat production has decreased by 1/5 over earth’s 4.6 billion year history > This is not a permanent energy source . .. 2. Residual Heat - related to heat produced in earth’s interior when earth first accreted. ( Pull of gravity on planetesmals and their collision) Want to know more about this? Take EAS 1601. The Heat within the interior can not build up indefinitely. 2 nd Law of Thermodynamics dictates that there will be a tendency for this heat to dissipate by traveling to the surface. This occurs by way of convection cells traveling through the mantle much like this our simple glass of water experiment also like the atmosphere’s general circulation These cells give rise to plate motion by way of mantle drag Like wind gives rise to surface ocean circulation . Once in motion other forces (see figure 6-21 in textbook) such as slab-pull keep plates in motion. Thus far we have been learning about what happens when plates collide. Now let’s we take a look at some of the major geological features that are produced as a result of these collisions: < Islands and Mountains Along Plate Boundaries; < Islands Chains, Seamounts, and Hotspots; < Cratons, Terranes, and Continents
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I. Volcanoes volcanic eruption brings magma to the surface to form “extrusive” igneous rock (Remember: non-volcanic magma forms “intrusive” or “plutonic” igneous rock.) Two types of classification schemes eruptive history active – erupted in historical times dormant – not active, but show no signs of erosion extinct - highly eroded topographic form shield volcanoes stratovolcanoes
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Lecture16 - EAS 1600 Introduction to Environmental Sciences...

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