20.docx

8/20 Earth: A Dynamic Planet Questions to Ponder What do we mean by ?dynamic? Planet? What processes make earth dynamic? What is differentiation and how is it exhibited? How do plate tectonics? System ? a group of interdependent materials Ex. A home plumbing system Controls on Dynamic behavior Physicals Laws Whatever you do, you can NEVER break these laws First and Second Laws of thermodynamics First Law (Conservation) Energy (matter) is neither created nor destroyed, but only changes form Second Law (Entropy) Systems move from High energy states to Low energy states (sometimes referred to as ?equilibrium?) Thus, Second Law helps explain: Why water flows downhill Why unstable minerals react or change to form more stable products Differentiation Separation of materials by various properties Density Size Thermal characteristics, etc. The solar system is differentiated Earth is differentiated Dynamic processes continue to differentiate materials Gravitational attraction forces heavier materials towards center. Differentiation: Earth scale When earth first formed, it was a molten, homogenous blob, but, as it cooled, remarkable changes occurred Heavier elements migrated towards center and formed ?core?; lighter elements formed crust (ex. Ice cube ?floats? on water) Earth?s lithosphere (Crust) is subdivided into two types Crust Continental crust Thicker than oceanic crust ? up to 75 km. Less dense ? 2.7 g/cm Strongly deformed Much older ? may be billions of years old Oceanic Crust Thinner than continental crust ? about 8 km More dense ? 3.0 g/cm3 Comparatively undeformed Much younger - < 200 million years old Composed of basalt