Ch 11 The Dynamic Planet The Pace of Change Geographic Time Scale Types of time a summary timeline of all Earth history o Relative the sequence of events based on the relative positions of rock strata above or below each other o Absolute actual number of years before the present Holocene name given to the youngest epoch in the geologic time scal the last 11 500 years Uniformitarianism environment today have been operating throughout geologic time The present is the key to the past assumes that the same physical processes active in the Earth s Structure and Internal Energy Earth is thought to have condensed from a nebula of dust gas and icy comets about 4 6 billion years ago Ga Australian zircons thought to be the oldest material on Earth Date back about 4 2 4 4 Ga Earth s Core and Magnetism Differentiated into the inner core and the outer core divided by a transition zone several hundred kilometers wide The fluid outer core generates at least 90 of Earth s magnetic field and the magnetosphere that surrounds and protects Earth from solar wind and cosmic radiation The average period of magnetic reversal is about 500 000 years Earth s Mantle Represents about 80 of Earth s total volume It is rich in oxides of iron and magnesium and silicates which are dense but get less dense towards the surface The uppermost mantle makes up the lithosphere Below this is the asthenosphere or plastic layer About 10 of the asthenosphere is molten which leads to tectonic activity Earth s Lithosphere and Crust Oceanic Crust Continental crust Moho discontinuity an important internal boundary between the crust and Lithosphere includes the crust and uppermost mantle the high velocity portion of the uppermost mantle that is a discontinuity essentially granite it is crystalline and high in silica aluminum potassium calcium and sodium It is relatively low density Denser than oceanic crust Isotactic rebound glacier melting and the crust rides higher in a recovery uplift This causes the entire crust to be in a constant state of compensating adjustment isotacy basalt It is granular and high in silica magnesium and iron when the load on top of a segment of crust goes away ie a The Rock Cycle Mineral an inorganic nonliving natural compound having a specific chemical formula and usually processing a crystalline structure there are about 30 rock forming minerals Silicate is one of the most widespread mineral families on earth Rock Three types of rocks igneous metamorphic and sedimentary an assemblage of minerals bound together Igneous rock one that solidifies and crystallizes from a molten state magma Magma is the intrusive form of the molten rock while lava is the extrusive form Make up approximately 90 of Earth s crust Pluton a general term for an intrusive igneous rock body regardless of size or shape that invaded layers of crustal rocks o Batholith the largest pluton formed An irregular shaped mass with a surface greater than 100 km2 Form the Sierra Nevada batholith o Sills small plutons that form parallel to layers of sedimentary rock o Dikes igneous rock that invades cross layers of other rock Felsic Igneous rocks derived both in composition and in name from feldspar and silica Felsic minerals are generally high in silica aluminum potassium and sodium High melting points Generally lighter in color and less dense than mafic rocks Mafic igneous rocks magnesium and ferric latin for iron Low in silica high in magnesium and iron and have high melting points Sedimentary processes sediments Lithification processes of cementation compaction and hardening of Derive from pieces of pre existing rock high energy sites have enough energy to transport the sediments The higher the energy the larger the sediment ie rivers Low energy sites don t have enough energy to transport the sediments therefor the sediment is deposited ie lakes Common rocks o Sandstone cemented sand o Shale compacted mud o Limestone lithified bones and shells or calcium carbonate that precipitated in ocean and lake waters o Coal ancient plant remains that became compacted into rock Stratigraphy the study of the sequence superposition thickness and spatial distribution of strata Chemical Sedimentary rocks Formed from dissolved minerals transported in solution and chemically precipitated from solution Limestone is most common chemical sedimentary rock Evaporates sediments left behind when water evaporates Metamorphic Processes Metamorphic rocks form when any rock either igneous or sedimentary is transformed by going though physical or chemical changed under pressure or increased temperature Foliated rock when the mineral structure demonstrates a particular alignment after metamorphism Plate Tectonics History Continental drift when plates shift because of moving fluid underneath Pangea most recent supercontinent One landmass encompassing all of the present day continents Plate tectonics include the processes of upwelling of magma lithospheric plate movements sea floor spreading and lithospheric subduction Sea Floor Spreading and Production of New Crust Mantle convection brings magma up to the crust causing the crust to fracture and the mantle is able to extrude onto the seafloor and cools to form new seafloor This builds up mid ocean ridges Subduction of the Lithosphere Subduction zone formed when continental crust and oceanic crust slowly collide The more dense oceanic crust slides underneath the continental plate Coincide with the earth s deep ocean trenches The subduction portion of the lithosphere travels down to the asthenosphere where it melts and becomes magma again which then rises to the surface Plate Boundaries Divergent boundaries o Characteristic of sea floor speading centers where upwelling material from the mantle forms new seafloor It is a constructional process Convergent boundaries o Characteristic of collision zones where areas of continental and oceanic lithosphere collide Zones of compression and crustal loss a destructional process Transform boundaries o Occur when plates slide laterally past one another at right angles to a sea floor spreading center usually WITH NOT VOLCANIC ERUPTIONS o No new crust is formed and no crust is subducted Earthquake and Volcanic Activity Primarily occur at plate boundaries Ring of fire surrounds the Pacific Basin Up welling of magma from the subducting Pacific plate causes increased volcanic activity Hot Spots Individual sites of upwelling material that come to the surface in tall plumes that produce