Introduction to Landforms The structure of the Earth Limited Understanding Crust Mantle depth less than 8 miles Understanding of earth s structure based on a minute fraction of total Good deal of understanding inferred by geophysical means Four regions of earth s interior Depth of 5km below ocean to near 20km below land Less than 1 of Earth s volume 0 4 of earth s mass Moho discontinuity significant change in mineral composition Extends to depth of 2900km 1800 miles Largest of four shells Make up of 84 of total volume 67 of total mass Three sublayers o Lithosphere o Asthenosphere o Rigid rocks lower mantle Outer Core Molten liquid o Not the source of lava Extends to depth of 5000km Earth s cores are the sources of energy that drive the slow movement o When rising pressure is low enough for it to melt otherwise its of hot rock through the mantle toward the surface convection solid Inner Core Earth s mass Magnetic Field Dense mass with radius of about 1450km Primarily made of iron nickel or iron silicate Two zones combined make up 15 of Earth s volume and 32 of Magnetic field of earth controlled by the outer core o Outer core turbulent convection of radioactive heating and chemical differentiation Similar to an electrical generator Which generate their own magnetic field Earth s conducting iron creates electric currents Plate Tectonics Magnetic poles not the same as the axial poles 1900 s theory pf continental drift Not a popular opinion in the scientific community 1960 s revived and expanded into the theory of plate tectonic o Accepted in the science community Land based clues to continental drift Land based clues to continental drift Geographical fit like a puzzle piece Geological old Mountain zones of matching ages appear as belts crossing southern continents Climatic Glacial deposits and rocks scratched by stones in moving ice show that ice covered huge tracts of the southern continents 300 mya Paleomagnetic Alignmnets of magnetized particles in old rock show Biological Identical fossil land plants and land animals crop up in the Evidence that lithosphere is broken into large slabs plates o Float on the asthenosphere Plate Boundary Movement o Driven by convection o Pull apart collide and slide past each other o Responsible for internal processes that southern continents all lay near the South Pole 300 mya southern continents now widely separated by sea faulting folding volcanic activity Minerals naturally formed compounds and elements of earth Classes of rock Igneous Sedimentary and Metamorphic Rock cycle including continental and oceanic plates Zhangye Danxia 24MYA Deposits of sandstone and other minerals The result similar to a layer cake was tilted by the action of the same tectonic plates responsible for creating parts of the Himalayan mountains Wind rain and time then sculpted extraordinary shapes Characteristics Inorganic Rocks Solid found in nature Specific chemical composition Contains atoms that arrange in patterns to form crystals Fewer than 20 minerals make up 95 of the composition of crustal Outcrops Bedrock Regolith Petrology characteristics of different rocks rocks Three Class of Rocks Igneous Sedimentary Metamorphic Igneous Rocks Igneous fiery inception o Magma molten rock beneath Earth s surface Pyroclastics o Lava molten rock when it flows onto Earth s surface o Fragments of rock erupted by volcanoes Igneous Rocks texture Classification of igneous rocks is based on mineral composition and Texture based on how rocks cool o Interlocking crystals formed as the molten rock cooled down o The smaller the crystals the faster the cooling Plutonic intrusive Sedimentary Rocks Volcanic extrusive thicknesses crystals are formed from shattered rock that was explosively ejected Surrounding rocks insulate the magma intrusion slowing cooling Individual minerals in a plutonic rock can grow to large size Rocks cool beneath Earth s surface Granite Form on Earth s surface Cool rapidly Generally do not show individual mineral crystals but can if the Basalt External processes cause rock disintegration Material transported by water as sediment Over long periods large amounts of sediment build to large Exert enormous pressure that causes particles in sediment to interlock Chemical cementation takes place Forms sedimentary rock Strata horizontal layers of sedimentary rock sometimes tilted into Most derive from the deposited remains of older rocks Composed of fragments of preexisting rocks Also known as detrital rocks Shale is an example Conglomerate composed of pebble sized fragments Formed by precipitation of soluble materials or complicated chemical Limestone and coal are examples Organic sedimentary rocks such as coal form from remains of dead vertical by Earth processes Rounded mineral grains joined by natural cements reactions Chemical and organic sedimentary rocks Clastic plants and animals Metamorphic Rocks changed by heat and pressure Regional metamorphism large volumes of rock are subjected to heat and pressure over long time scales Rocks that were originally igneous or sedimentary and have been Causes a cooking of rocks Rearranges the crystal structure of the original rock Contact metamorphism rock contacts magma and is rearranged Limestone becomes marble Sandstone becomes quartzite Shale becomes slate Metamorphic rocks with narrow foliations Broad banded foliations Processes where rocks can transition between the three rock types Sedimentary rocks make up 75 of the continents Continental crust sial silicon and aluminum Ocean floor crust sima silicon and magnesium Ocean lithosphere is more dense than continental lithosphere Ocean crust can be subducted into the asthenosphere Recognition of differences between oceanic crust continental crust Schist Gneiss The rock cycle CONTINENTAL AND OCEAN FLOOR ROCKS Sedimentary cover is not thick Isostasy The study of characteristics and development of landforms Structure Process Slope Drainage and mantle Geomorphology Basic Elements Fundamental Questions What where why so what STRUCTURE PROCESS Nature arrangement and orientation of the materials making up a landform Is it composed of bedrock if so what kind If not what are the nature and orientation of the sediments or other depositions o Deposition and Erosion Combined actions that produce the landform Combination of geologic hydrologic atmospheric and biotic processes Or from one process Process o Glaciation Slope Fundamental aspect of Shape of any landform A reflection of the balance