GEOL 101 Exam 2 Study Guide Lectures 8 12 Lecture 8 Deformation the folding faulting shearing compression and extension of rocks Tensional forces stretch rocks Compressive forces push rocks together Shearing forces pushes 2 parts of a rock formation in opposite directions Representing Deformation on a map Strike compass direction of a layer of rock where it hits the surface Dip angle below the horizontal perpendicular to the strike Cross sections what the earth would looks like if you cut a vertical slice through the earth Types of deformations faults a fracture that displaces two sections of the same rock Dip slip the rocks move up or down the dip of the fault compressive or tension forces Strike slip the rocks move laterally to each other shearing forces joints fractures in a rock that do not displace it folds sedimentary layers are bend in a curved manner Anticlines bend upwards like a hill Synclines bend down like a valley Basin Sedimentary beds dip toward a central point in a circular structure sediments can gather in the basin Dome circular anticline of rock layers Styles of deformation Tensional when plates pull away from each other the earth stretches and creates a rift valley where faults occur and blocks of rock drop down Compressional when one plate slides over another it creates a huge thrust fault pushing up massive amounts of rock creating mountains Shearing can be very complex and can combine with tensional and compressional forces This greatly increases the likelihood of earthquakes due to all the increased activity Lecture 9 Dating measuring the absolute age of an event in the Geological Record in terms of of years ago Relative age age in terms of weather one rock was formed earlier or later than another Stratigraphy study of layers in rocks 1 Principal of original horizontality sediments are deposited by gravity in horizontal layers 2 Principal of superposition each layer is older than the rock layer over it and younger than the layer under it The order of these layers is called stratigraphic succession The principal of faunal succession fossils found in an ordered sequence of age can be used to match fossil sequences in other outcrops across the world The study of fossils is called paleontology Unconformities are where one rock layer meets another rock layer It is a gap in the geological record Disconformity is where 2 parallel Sedimentary beds meet each other Nonconformity is where a Sedimentary bed is deposited onto an Igneous or metamorphic basement rock Angular unconformity is when sediments are deposited on folded bed that has been eroded away All these unconformities can shift and cause cross cutting relationships that can be used to observe the history of how the geological region was formed Geological time scale history of geological events Eras most basic divisions of Geological time Paleozoic Mesozoic Cenozoic Periods subdivisions of Eras Ephochs some periods have so much activity that they are further divided into epochs Isotopic clocks Isotopic dating looking at the decay of elements that occur naturally in rocks Measured by the half life of an element which is the time it takes for half of the radioactive material to decay This is recorded by looking at the ratio of parent radioactive material atoms to daughter stable atoms Lecture 10 Big Bang Universe is thought to have been formed by a cosmic explosion 13 7 Billion years ago Nebular Hypothesis theorizes that the Solar system that earth is a part of was formed by a rotating cloud of gas and dust 4 5 Billion years ago that contracted and formed the sun and planets The terrestrial planets are those that are closest to the sun mercury Venus Earth Mars and made of rock These were formed by accretion of planetesimals which collided and stuck together Heavy Bombardment a time when many planetesimals were striking the surfaces of the terrestrial planets followed by the late heavy bombardment followed this The first life on earth has its origins shortly after the end of the late heavy bombardment The moon was formed when a large mars size body struck earth and the debris from this planet started orbiting earth These satellites clumped together to form the moon This collision had enough energy to melt earth and cause the densest material to move to the center creating the iron core and the lighter material moved to the surface to create the crust Craters on the moon and other planets without many erosion factors can be dated by looking at craters New geological surfaces have few craters while old surfaces have many craters All the terrestrial planets differ vastly in terms of composition because of their different distances from the sun Mercury is similar to that of earth s moon and is relatively unstudied Venus is similar to earth in that it has plate tectonics but they are vastly different in the way they work They are called flake tectonics and are formed by heavy volcanism that forms a thin crust that is recycled often therefore is very young Mars has a surface very similar to that of earth but has been tectonically inactive for 3 Billion years Its surface shows evidence that water once existed there Lecture 11 Tectonic provinces Shields exposed Precambrian rock in a continent that is tectonically stable Platforms stable basement rock covered by layers of flat lying sediment Phanerozoic Orogens areas where large amounts of rocks have been deformed by plate collisions and formed mountains Continental basin area where sediments have subsided and created a bowl shaped area Extended crust region where deformation causes crust to thin Continental Growth Magmatic Addition vertical process in which magma is transported to the surface and create magma chambers which become part of the continental crust this can also happen at active continental margins Accretion horizontal process in which island arcs attach themselves to continents when during subduction or collision Orogeny the process of mountain building by folding faulting magmatic addition and metamorphism This tends to occur on the edges of cratons The Wilson Cycle the cycle of oceanic basins opening and closing via rifting and then converging The reason that Cratons last so long in comparison to oceanic basins is that they are much less dense than oceanic rock Lecture 12 Geobiology the study of how biology interacts with the earth The Biosphere is divided into ecosystems which are further divided into producers produce own food from sunlight CO2 and