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Chapter 11 Outline

Chapter 11 Outline - chapter 11 the dynamic planet...

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chapter 11: the dynamic planet Introduction One task of phys geog- explain spatial implications of new info we have gained & its effect on the landscape; endogenic forces- internal to Earth, driven by radioactive heart derived fr sources w/in planet; activates surface fractures, mountain building, earthquakes, volcanoes the pace of change Geologic time scale - summary timeline of all Earth history-eons, eras, periods, epochs; earth 4.567 bil yrs old; depicts 2 impt kinds of time: relative (what happened in what order) & absolute (actual # of yrs before the present); rel time based on rel positions of rock strata above/below each other… Based on impt principle superposition -rock and sediment always arranged w/youngest beds super- posed toward top of rock formation and oldest at base, if not disturbed; study of thse sequences- stratigraphy ; Holoclene = present epoch; fossils embedded in strata- clues Scientific methods eg radiometric dating determine absolute time => let scientists actively update geologic time- more accurate; fund’tl principle of Earth science- uniformitarianism - assumes the same phys processes active in envt today have been operating thruout geologic time Supported by evidence; advocated by James Hutton, Charles Lyell; catastrophism claims Earth is young & mountains, canyons, plains formed thru catastrophic events that didn’t require eons of time- mere belief b/c little evidence; w/uniform’m, catastrophic events can punctuate time eg earthquakes: These occur as interruptions in the generally uniform processes slowly shaping the landscape; this= concept of punctuated equilibrium earth s structure and internal energy Possibly oldest materials in Earth’s crust- detrital zircons in W Australia, ~4.3 billion yrs old; tell us Earth forming cont’tl crust at least 4 bil yrs ago, during Archean Eon; as Earth solidified, gravity sorted materials by density; heavier things center, lighter surface, crust Earth’s interior sorted into concentric lyrs, w/diff chem. composition/temp; heat energy goes center out by conduction, phys convection in the more fluid/plastic lyrs in mantle nearer surface; knowledge of earth’s internal differentiation into thse lyrs gotten thru indirect evidence: Telling properties: cooler, more rigid areas transmit seismic waves @higher velocity than hotter areas; this= science of seismic tomography ; density affects seismic-wave velocities too- plastic zones actually absorb some; some seismic waves reflected/refracted, change velocities as densities change.. This info used by seismologists to help deduce Earth’s structure; Earth center surface distance 3963 mi; cont’l crust thickness ~20 mi Earth’s Core and Magnetism 1 / 3 of Earth’s mass, 1 / 6 of volume lies in its dense core - differentiated into inner/outer core , divided by 100s kms wide-transition zone; inner core ~iron- very high temp, solid only b/c of grt pressure; inner core ~formed 1 st after Earth condensed; its iron impure- combo’d prob w/silicon, O 2 , sulfur
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