Robert W. ChristophersonCharlie ThomsenChapter 11The Dynamic PlanetThe seemingly static landscape and mountains are constantly being shaped and reshaped by endogenic and exogenic forces, although slowly. Given enough time, any slow process can make a difference. The Pace of ChangeEarth’s Structure and Internal EnergyThe Geologic CyclePlate TectonicsThe Dynamic PlanetGeologic time scalePopular time: 1500 BC, 2009ADYears Before Present (BP): Uniformitarianism: An assumption that the same physical processes active in the environment today have been operating throughout geologic time.The Pace of ChangeGeologic Time ScaleFigure 11.1Earth age: 4.6 billion yearscondensed and congealed from a nebula of dust, gas and icy comets.Scales of Geologic TimeEons: Eras: Periods: Epochs: Zoic: lifeProtero-: former, anteriorPhanero-: visible to the naked eyeflowering plantsPaleo-: oldMeso-: middleCeno-: recentAtom:nucleus: protons (+) & neutronselectrons (-)For some matter, its protons and neutrons do not stay together indefinitely. The particles can break away and the nucleus can disintegrate and form new matter, in the mean time release radioactive energy. The decay rate is measured by half time, the time needed for the matter to decay half of its mass into new matter.Measuring the ratio of original matter and its decayed matter, one can estimate the ago of the object.The oldest rock dated: 4.3 b.y.a, indicating continental crust was forming this many years ago.Earth’ Time Clock: RadioactivityEarth’s Core : Inner CoreOuter CoreEarth’s Mantle:Lower MantleUpper MantleAsthenosphereUppermost MantleCrustEarth’s Structure and Internal EnergyEarth in Cross SectionFigure 11.2Earth’s InteriorFigure 11.2Earth’s InteriorFigure 11.2Inner core remains solid iron because of tremendous pressure though temp well above melting point, Outer core generate 90% of Earth magnetic field to form magnetosphere, which protects Earth from the solar wind and cosmic radiation.Mantle includes lower and upper (upper mantle, asthenosphere and uppermost mantle) mantle, representing 80% of Earth volume. Temp increase with depth. Rich in oxides of iron, magnesium and silicates.Note the density gradientAs Earth solidified, gravity sorted materials by density. Heavier substances (e.g. iron) gravitated toward the center; lighter elements (e.g. silica) welled upward to the surface.Figure 11.2Earth’s InteriorLithosphere: Crust + uppermost mantle.Asthenosphere: plastic layer (least rigid in mantle), contains hot spots causing vertical convection, creates tectonic activityContinental crust: primarily granite high in silica, aluminum, potassium, calcium and sodiumOceanic crust: primarily basalt high in silica, magnesium and ironCore to CrustFigure 11.3Scientists cannot dig that deep. The deepest hole scientists ever dug is 12.23km (20 years of effort!)Scientists infer the deep Earth structure indirectly through seismic tomography. The rate of transmittance of seismic waves depends on the density of the structural material. Rigid matter transmits the seismic waves faster. Plastic zones simply do not transmit certain seismic waves. Some seismic waves are reflected when density changes, whereas others are refracted (or bent) as they travel through Earth. How Scientists Know the Deep Structure? At least 90% of Earth’s Magnetism is generated by fluid outer core. Magnetic North is at 83o N, 114oW in 2005. Magnetic north pole migrates. It moved 1100 km in the past century. Magnetic reversal: Magnetic polarity sometimes fades to zero and returns to full strength with magnetic poles reversed. It happened 9 times in the past 4 million years. The transition period between reversal is relatively short (1,000 ~10,000 years) Current records indicates that magnetic fields decay over the last 150 years. We may be within 1000 years of magnetic reversal.Earth’s MagnetismIsostaticAdjustmentFigure 11.4Continental crust is lightest, “floating” on denser layers. When there is heavier loads, such as mountains, glaciers, , the crust “sink” deeper (like a boat loaded with cargo). Unloading these cargos will results in isostatic rebound as shown here.GPS can be used to study the rate of isostatic rebound. A group of scientists from UAF found that southern Alaska is rebounding much faster than they thought because of melting of glaciersRock CycleMinerals and RocksIgneous ProcessesSedimentary ProcessesMetamorphic ProcessesThe Geologic CycleThe Geologic CycleFigure 11.5The cycle of matter within the Earth system caused by exogenic and endogenic forces.Hydrologic CycleRock Cycle Tectonic CycleThe Geologic CycleFigure 11.5Eight natural elements make up 99% of Earth’s crust! Oxygen and Silicon make up 74.3%. There are more Oxygen in the crust (47%) than in the atmosphere (21%) !The Rock CycleFigure 11.6A Brief HistorySea-Floor Spreading and Production of New CrustSubduction of the CrustThe Formation and Breakup of PangaeaPlate BoundariesEarthquake and Volcanic ActivityHot SpotsPlate TectonicsFirst person to notice the apparent fit of some continental coastlines was a Geographer (Abraham Ortelius) in 1500s.The “continental drift” concept was formally introduced by a German geophysicist, Alfred Wegener in 1915. The Earth had a single giant continent, Pangean 225 MBP, then drifted apart as we have today.Wegener’s continental drift concept was confirmed in the 1960s.A Brief History of Plate TectonicsCrustal Movements: Sea Floor SpreadingFigure 11.13A remarkable feature of the sea floor:An interconnected worldwide mountain chain, forming a ridge ~64,000 km in length and ~1,000 km in width.Magnetic ReversalsFigure 11.14Evidence of sea floor spreading: 1. The magnetic particles orient themselves in line with the magnetic fields when thelava appeared and its orientation is frozen in the rocks. 2. Radioactive dating: the farther away from the ridge, the older the age of the rocks.Relative Age of the Oceanic CrustFigure 11.15The oldest sea floor rock is 208 MBP (quite young compared to 4.6 Billion years of Earth).Continents AdriftFigure 11.167 major plates:Three kinds of plate boundaries:Earth’s Major PlatesFigure 11.17Arrows represent 20 million years of movement.Earthquakes and VolcanoesFigure 11.20Plate boundaries are the primary location of earthquake and volcanic activity: upwelling material arrive at the surfaceHot Spot TracksFigure 11.21Another hot spot: Yellow Stone National Park: a mega-magma