Plate Tectonics Flashcards
How old is the earth?
Over 4.5 billion years old
Name the structure of the earth in order from exterior to the centre
Crust- oceanic and continental
Mantle or asthenosphere
Outer core
Inner core
Name the characteristics of the crust
- 0-70km thick, coolest and least dense rock
- rocks are rich in sodium, silicon, aluminium and potassium
- it’s divided into continental crust and oceanic crust
What are the properties of continental crust?
- it’s old, over 1500 million years old
- it’s permanent
- less dense
- mainly granite, silicon, aluminium and oxygen
What are the properties of oceanic crust?
- younger, less than 200 million years old
- it is created so it can be destroyed
- 6-10km thick and is denser so it can sink
- mainly basalt silicon magnesium and oxygen
What are the properties of the mantle?
- 2900km thick
- apart from the rigid upper mantle, most of the mantle is semi molten containing lighter elements of silicon and oxygen
- temperatures reach 5,000 degrees C and generate convection currents
What are the properties of the core (inner and outer)?
- hottest part of the earth, over 5,000 degrees C
- outer part is liquid and the inner is solid
- the inner is made from iron and nickel ore
What is the name of the discontinuity found at the top of the mantle?
Mohorovicic boundary
What does the mohorovicic boundary do?
Separates the mantle from the crust
The crust and part of the mantle beneath form…
Large plate like areas of the lithosphere which float upon the soft and ductile material known and the asthenosphere
What are the crust and the upper most part of the mantle?
A single unit
What are the two processes that heat from the core is produced?
- Primordial heat left over from the earths creation
- Radiogenic heat produced by the radioactive decay of isotopes
What isotopes contribute to the radioactive decay?
Uranium -238
Thorium- 232
Potassium-40
What does the theory of plate tectonics help us understand?
- distribution of the worlds major landforms
- where natural hazards can strike
- the distribution of minerals and energy supplies
How many plates is the earth made up of?
16
Do plates move? If so, how much?
Yes, a few centimetres per year
What was the earth beloved to be like 300 million years ago?
One super continent called Pangea
In the 16th century, who was the first to recognise the continents could be fitted together?
Francis Bacon
Who came up with the idea of continental drift in the 20th century?
Alfred Wegener
When did wegener state the plates began to move apart?
In the Carboniferous age 250 million years ago to sometime in the Pleistocene age about 1 million years ago it was a single continent that began breaking up and drifting apart
What evidence supports wegener’s theory of continental drift?
- Rare fossils found in rock across oceans in different continents
- glaciations affected different areas becoming contiguous if the continents are fitted back together
- rocks, mountain ranges and fold belts are all consistent within the reconstructed super continent
What was discovered during the 1960’s-70’s that caused doubts in Wegeners theory?
- when volcanic rocks cool they adopt a magnetic orientation which reflects the earth magnetic field
- when taking a transept along the ocean floor, it was found that rocks paleognetism vary, like the ocean floor was formed at different times, patterns either side of the oceanic ridge were identical
It became clear that rocks relating to each magnetic phase could be traced linearly along the ocean floor, like a band parallel to the ocean ridge so…
It was clear that as the crust of the mid Atlantic ridge split, and the ocean floor moved apart, new rocks were being created in the gap
What is another term for a destructive boundary?
Convergent
What is another term for a conservative boundary?
Transform
What’s another term for a constructive boundary?
Divergent
Explain convection currents in the mantle
- Crust isn’t stable so the plates are able to move
- heat in the mantle is obtained through radioactive decays and primordial decay which creates convection currents
- mantle is semi molten so hot liquid rises and it is less dense the cool liquid sinks as it is more dense
- this causes a continuos current which moves the plates above
Explain gravitational sliding, ridge push and slab pull
- The lithosphere thickens with…
…distance and time away from the mid-ocean ridge
Explain gravitational sliding, ridge push and slab pull
- This is because it cools with…
…distance and the boundary between the solid lithosphere and plastic asthenosphere becomes deeper.
Explain gravitational sliding, ridge push and slab pull
- The result of the thickening with distance from the ridges is that…
…the lithosphere/asthenosphere boundary slopes away from the ridge
Explain gravitational sliding, ridge push and slab pull
- Gravity acting on the weight of the lithosphere near the ridge…
…pushes the older part of the plate in front, this is ridge push
Explain gravitational sliding, ridge push and slab pull
- Furthermore, following subduction the lithosphere sinks into…
…the mantle under its own weight, helping to pull the rest of the plate with it, this is slab pull
