HE 1.1

• Describe the characterisitics of the three main layers of the basic stucture of the earth (3) - Core, matle and crust - Mantle and the core seperate at a depth of 2900km - The boundary between the mantle and crust is called the mohorovic district
• Describe the lithosphere in terms of the basic structure of the earth (2) - Makes up the crust and tre rigit upper part of the matle - Section of the earth that gets divided into oceanic and continental plates
• Describe the asthenosphere in terms of the basic structure of the earth (2) - Lies beneath the rigid upper part of the mantle and is in a semi-molten state due to high pressures and temperatures - Within this layer convection currents occure due to heat generated by mantle, these currents carry the solid lithosphere which lies above
• 4 stages of the ridge push mechanism (divergent plate boundaries) in terms of the basic structure of the earth 1. As plates diverge molten magma rises at a mid ocean ridge at a very high temperture heating the rock around it 2. Crust ridge is heated and as it expands it becomes less dense, becoming more elevated above surrounding sea floor 3. New crust formed at the plate boundary then starts to cool and becomes denser 4. Gravity causes the older denser crust to slide away from ridge, exerting force on tectonic plates, causing them to spread
• 3 Stages of the slab pull mechanism (convergent plate boundaries) in terms of the basic structure of the earth 1. Crust that is pushed away from divergent boundaries by ridge push cools and becomes denser 2. Crust eventually becomes denser than underlying hot mantle and starts to sink under its own weight 3. As crust sinks into the mantle it pulls the rest of the plate along with it where it is then destroyed
• What does the slab pull mechanism produce in terms of the basic structure of the earth - Creates oceanic trenches and subduction zones
• What is the evidence of sea floor spreading (3) - Continental drift - paleomagnetism - Age of sea floor crust
• Describe continental drift in terms of evidence for sea floor spreading (2) - 1912 Alfred wegener published the theory of continental drift suggesting their was a single super continent called pangea 250 million years ago - The continent then split into Laurasia and Gondwanaland
• Describe the two forms of Wegeners evidence for continental drift in terms of evidence for sea floor spreading - Biological and geological
• Describe the geological evidence for continental drift in terms of evidence for sea floor spreading (3) - Glacial deposit from 290 million years ago found in South America, Antarctica and India - cannot be explained by current position and must have formed when all continents were joined together - Mountain chains and rock sequences on either side of oceans are similar, like those in north canada and north scotland - The fit of the continents like south america and africa on either side of the atlantic ocean
• Describe biological evidence for continental drift in terms of evidence for sea floor spreading (3) - Fossilised remains of plants have been found in India and Antarctica - Similar fossil brachiopods found in Australian and Indian limestone - Similar fossil reptiles found in south and north America
• Describe the process of paleomagnetism in terms of evidence for sea floor spreading (4) 1. Iron particles found in lava align with earths magnetic field 2. Lava solidifies providing a permanent record of earths magnetic field at the time 3. Earths polarity reverses every 400,000 years resulting in a series of magnetic stripes with rocks aligned alternatively towards north and south pole 4. This striped pattern is mirrored on either side of mid oceanic ridge suggesting that oceanic crust is slowly spreading away
• What does paleomagnetism imply is happening to the rocks in terms of evidence for sea floor spreading - Sea floor is spreading, but earth isnt increasing in size, so the tectonic plates must be getting destroyed (slab pull mechanism)
• Describe the Age of Sea floor crust as a means of evidence of sea floor spreading (2) - 1960's ocean drilling programme revealed thickest and oldest sediment was found further from mid atlantic ridge - No rock was older than 200 million years, confirms that crust is eventially destroyed in subduction zones
• What are the types of Plate boundaries/margins - Divergent Plate Boundaries - Conservative plate margins - Convergent plate boundaries
• Describe where divergent plate boundaries mainly act At mid ocean ridges
• Describe mid-ocean ridges with regards to features at divergent plate boundaries - On average 2.5 km below ocean surface consisting of long mountain chains in places rising 3km above seabed - Broken into segments by transform faults where no volcanic activity takes place
• Describe the features of mid-ocean ridges with regards to features at divergent plate boundaries (2) - Pillow lava - Eruption of magma occurs underwater directly onto the seabed where it is cooled rapidly forming rounded mounds - Black smokers - Sea water seeps in to rifts where it is superheated and rises to the surface causing chemical changes in basaltic rock with metal sulphides causing the black colouring
• Describe the formation of islands along mid ocean ridges with regards to features at divergent plate boundaries (2) - Magma rises to the surface forcing overlying rocks up into the dome, rigid lithosphere fractures under pressure along parallel faults - This then produces underwater rift valleys where magma upwells to form volcanic islands (like iceland)
• What two processes occur at mid ocean ridges with regards to features at divergent plate boundaries - Formation of volcanic islands - Rifting away from mid ocean ridges
• Describe the process of rifting away from mid ocean ridges with regards to features at divergent plate boundaries (2) - If the oceanic and continental crust is considerably thin then rifting can occur, where the crust is stretched causing faulting - This forms a sunken valley known as a graben with risen horsts either side - an example is the red sea rifting northwards towards turkey
• Describe conservative plate boundaries (2) - Where tectonic plates neither converge or diverge, but instead slide past each other in a shearing motion - Volcanic activity is consequently absent, however frictional resistance to movement builds up at these boundaries, sometimes these rocks fracture from the pressure causing earthquakes
• Describe the features at a conservative plate margin (2) - Drainage is modified as river courses are deflected by movement along the fault line - An example is the san andreas fault where north american and pacific plates slide past one another
• What are the three ways tectonic plates collide together and converge with regards to features at Convergent plate boundaries - Oceanic to continental - Oceanic to oceanic - Continental to continental
• Describe the processes which occur at oceanic to continental boundaries with regards to features at Convergent plate boundaries (2) - Denser oceanic plate is subducted under less dense continental plate forming a oceanic trench - The angle at which the oceanic plate is subducted is between 30 and 70 degrees
• What is a benioff zone with regards to features at a oceanic-continental convergent plate boundary - The boundary between subducting ocean plate and overriding continental plate at a convergent boundary
• Describe the features at a oceanic-continental boundary with regards to features at Convergent plate boundaries - Formation of fold mountains - where sedimentary rocks crumples and is uplifted along leaning edge of continental plate, the contiental plate is buckled and uplifted with vast amounts of moltern material injected into it
• Describe the processes which occur at oceanic to oceanic plate boundaries with regards to features at Convergent plate boundaries - The slightly denser of the two oceanic plates will subduct under the less dense one, this will also form a oceanic trench
• Describe the features that form at oceanic - oceanic plate boundaries with regards to features at Convergent plate boundaries - Islanks Arks formed when descending plate melts and magma rises to the surface forming chains of volcanic islands
• Describe the process that occurs at continental-continental plate boundaries (1) - Where the two continental plates converge little subduction takes place as the plates have very similar densities
• Describe features of continental - continental plate boundaries with regards to features at Convergent plate boundaries - Fold mountains - including the himalayas, alps
• Describe the ring of fire in terms of convergent and conservative plate boundaries (2) - Pacific ocean is largely bordered by convergent and conservative plate boundaries, 80% of all earthquakes and volcanoes are located here - Trenches, island arks are some of the physical features located here