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Earth Materials – Geology Plate tectonics. Why have all the mountains not worn away by now?. Earth Structure. Radius 6300-6400km Thin crust Mantle extends almost halfway to the centre The core makes up the rest. Composition. Low density solid crust floating on an almost solid mantle

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earth materials geology plate tectonics

Earth Materials – GeologyPlate tectonics

Why have all the mountains not worn away by now?

earth structure
Earth Structure
  • Radius 6300-6400km
  • Thin crust
  • Mantle extends almost halfway to the centre
  • The core makes up the rest
composition
Composition
  • Low density solid crust floating on an almost solid mantle
  • But overall the Earth is dense
  • The core must be very dense
  • Probably made of dense metals nickel and iron
  • Hot liquid outer core and solid inner core
rock cycle
Rock Cycle
  • Weathering breaks down the rocks
  • Erosion wears them into smaller pieces as they are transported towards the sea
deposition of sediments
Deposition of sediments
  • Most sediments settle in water
  • Currents and waves form ripple marks
  • Evidence can be found for this in the rock
  • Ripple marks can be preserved in the rock
sedimentary rocks
Sedimentary rocks
  • Grand Canyon
  • Youngest rocks at the top
  • Rocks and fossils older as you go down
unstable earth
Unstable Earth
  • The Earths crust is subjected to huge forces
  • Very large forces can fracture the rock
  • This can be seen as fault lines in the rock layers
tilted and folded
Tilted and Folded
  • Sedimentary rocks are often found tilted
  • They can also be folded by the huge forces
  • This has happened at Lulworth cove
  • Sometimes the rock layers can even be turned upside down
alfred wegener
Alfred Wegener
  • Some people thought the Earth was shrinking and cracking
  • Wegener thought whole sections of the crust moved (plate tectonics)
  • Some people did not understand and thought the continents floated around in the oceans (continental drift)
  • He died before people accepted his ideas
evidence
Evidence
  • Same fossils and rocks found in different parts of the world
  • Africa and South America look like pieces of a jigsaw
earthquakes
Earthquakes
  • Plates moving in any direction causes earthquakes
  • The worst are caused by plates rubbing past each other as in C
  • This happens along the Californian coast
sea floor spreading
Sea floor spreading
  • Large continents begin to crack and split apart
  • The gaps fill with water
  • Small seas become oceans
  • The mid ocean ridge continues to produce new crust
why spread
Why spread?
  • Why is the Atlantic still getting wider
  • The plates are pulled apart by convection currents in the mantle below
  • Caused by heat released from natural radioactive processes
  • At the mid Atlantic ridge molten rock from below rises up to fill the gap with new basaltic rock
more evidence
More evidence
  • More evidence has been found for Wegeners theory
  • The Earths North and South pole have flipped many times
  • These leaves magnetic ‘stripes’ in rock containing iron minerals
so the earth must be growing
So the Earth must be growing?
  • Dense heavy oceanic crust can be subducted below less denser continental crust.
  • The friction melts rock
  • This magma rises through the crust to form new volcanoes
  • This is happening in South America (The Andes)
continents collide
Continents Collide
  • Eventually when plates move together the continental crust collides
  • The heat and pressure make metamorphic rock
  • It also pushes and folds the rocks into high mountains
  • The Himalayas rise to 8848m and are still growing today
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