Geography Lectures - Lecture 1 Jan 18 The dynamic planet...

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Lecture 1- Jan. 18 The dynamic planet The pace of change Geological time scale- summary timeline of all earth history. The 6 major extinctions or depletions of life forms are shown. Earth is 4.567 Ga (billion years old), moon is 30 million yrs younger (4.537 Ga), formed when a mars sized object struck planet earth. Two types of time: A. relative (what happened in what order) & B. absolute (actual number of years before the present) 88% of geological time occurred during the Precambrian Eon. Uniformitarianism- the same physical processes operating in the environment today have been operating throughout geological time. Ex: if a stream carves valleys now it must have done so 500 Ma or 1 Ga. Earths Structure and internal energy Earth is thought to have condensed and congealed from a nebula of dust, gas, and icy comets~4.6 Ga. Oldest rocks on earth Acasta Gneiss in NW Canada-3.96 Ga Detrital zircons in W Australia-4.3 Ga Earth forming continental crust atleast 4 Ga Materials sorted by density as earth solidify Heavier substances such as iron gravitated to its center, lighter elements such as silica welled upward to the surface. This led to differentiated layers. Earths interior: inner core, outer core, lower mantle, and upper mantle (in order from center of earth) Earths mantle- represents 80% of earths total volume. Mantle is rich in oxides of iron, magnesium, and silicates. Dense and tightly packed at depth.
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Uppermost mantle, along with the crust, makes up the lithosphere, 45-70 km thick. Discontinuity- place where physical differences occur between adjoining regions of earths interior, i.e., between outer core and lower mantle. Upper mantle divides into 3 layers: upper mantle, asthenosphere, & uppermost mantle (high velocity zone) Earths Lithosphere and crust Uppermost mantle along with the crust make up the lithosphere. Mohorovicic discontinuity- boundary between crust and high velocity portion of upper mantle. Continental crust- made up of granite (Sial- Si lica & al uminum) Ocean crust- made up of basalt (Sima- si lica & ma gnesium) The distance from Anchorage to Ft. Lauderdale is the same distance between earths core and its outer crust. Bouyancy- Something less dense floats in something more dense. Buoyancy Isostatic Adjustment Earths entire crust is in a constant state of compensating adjustment. It is being formed, deformed, moved, and broken down by physical, chemical, and biological processes. Examples: Mountain mass slowly sinks, displacing mantle material. Because of the loss of mass through erosion & transportation, the crust isostatically adjust upwards and sediments accumulate in the ocean. The Geological Cycle
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This note was uploaded on 03/21/2011 for the course POLITICAL 1101 taught by Professor Staff during the Spring '11 term at Georgia State.

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Geography Lectures - Lecture 1 Jan 18 The dynamic planet...

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