1. Plate Tectonics & 2. Plate Boundaries Flashcards
Inner Core
- Solid
- 90% iron, some nickel and sulphur
- 1220km thick
- 5,500 degrees
The outer core
- Fluid, molten
- Iron and nickel
- 2,400 km thick
- 3,000-4,000 degrees
The upper mantle
- Just beneath crust
- 410km deep
- Mostly solid rock, but some areas are molten
- Divided into the lithosphere and asthenosphere
Lithosphere
- The lithosphere included the crust and the brittle upper portion of the mantle
- Rigid
- 5-2000km in depth
- Consists of the plates
Asthenosphere
- Denser and weaker layer below the lithosphere
- 100-200km deep
- Temperature and pressure is so high that the rocks are semi-molten and more ductile
Ductile
The ability to bend or deform without fracturing
The lower mantle
- 600-2700km in depth
- Hotter and denser than upper mantle
- Less ductile
- Solid rock
Moho line
The division between the crust and mantle
The crust
- Outermost layer of Earth’s structure
- 1% of Earth’s mass
- Solid rocks and minerals
- Oceanic and continental crust
Oceanic crust
- Thin (5-10km)
- Denser/ heavier
- Basalt rock
- Sima (silica and magnesium)
Continental crust
- Thick (up to 70km)
- Less dense/ lighter
- Granite
- Sial (silica and aluminium)
Who discovered continental drift?
Alfred Wegner 1912
Who discovered continental drift?
Alfred Wegner 1912
Who discovered convection currents?
Arthur Holmes 1928
Who discovered mid-ocean ridges?
Maurice Ewing 1947
Who discovered sea-floor spreading?
Harry Hess 1962
What is the theory of continental drift?
- Suggests the plates were constantly moving by convection currents
- Wegner proposed there was once a supercontinent, known as Pangaea
- Approx. 200 million years ago Pangaea began to break apart
What evidence exists in favour of continental drift?
- Continental fit
- Matching Plant fossils
- Matching Animal Fossils
- Matching rock folds and mountains (Appalachians and Caledonians)
- Glacial Deposits (in Africa and Australia are too hot)
What is the theory of convection currents?
- Wegner died before being able to prove continental drift
- Holmes suggests that magma deep in the mantle becomes superheated by the 6000 degree core.
- As the magma becomes hotter, it rises towards the crust
- Upon reaching the mantle it becomes semi-molten, then moves laterally before sinking again.
- As it moves sideways it rubs off the lithosphere which leads to the plates separating, colliding and sliding past each other.
What is the theory of mid ocean ridges?
- Maurice Ewing discovered a chain of underwater volcanoes and mountains in the Atlantic
- He also discovered that the ocean floor is made of basalt and is thinner closer to the ridge
What is the theory of sea-floor spreading?
- Harry Hess added to discoveries made by Ewing, by discovering mid-ocean ridges is where new sea floor was made
- Magma pushed up through the separating plates hardens and creates new ocean floor
- The Atlantic began to open 130 mya and still is
What evidence exists supporting sea-floor spreading?
Age of the sea floor- Progressively older the further from the ridge. 10 mya beside ridge, 130 mya near continents
Ocean Sediments- Ocean floor further away from ridge has thicker sediment
What are the evolving theories of plate tectonics?
Slab pull, Ridge push, Mantle Plumes
What is slab pull?
- Negative buoyancy of a plate causes subduction
- As a plate becomes negatively buoyant, the plate cools and begins to subduct under the less dense plate
- The stress is moved up through the lithosphere, pulling it along the surface by slab pull
What is ridge push?
- Mid-ocean ridges form as tension forces at divergent plate boundaries
- Tension forces are caused by plates separating, as plates become thin, cracks or fissures can form. Hot mantle rock will flow up to fill the space.
- As the mantle Rick rises, it reduces in pressure. The melting of the mantle turns it into magma. This magma injects into the plate, cools and becomes new crust
- This pushes the ridge apart by ridge push.
What are mantle plumes?
- A mantle plume is a large column of hot rock that rises through the mantle
- The heat from the plume causes rock in the lithosphere to melt, this results in magma chambers
- When these plumes reach the crust, they form diapirs (also known as hot spots) e.g. volcanic islands like the Canary Islands and Hawaii.
What are convergent/ destructive plate boundaries?
Two plates colliding
What are divergent/ constructive plate boundaries?
Two plates separating
What are transform/ passive plate boundaries?
Two plates sliding past each other
What are endogenic forces?
Endogenic forces are internal forces within the earth that effect landscape on earth’s surface
