Plate movement Flashcards
What are sedimentary rocks
Rocks created through compaction and cementation of layers of particles
What are Metamorphic rocks
Rocks created through the heating and applied pressure of particles underground
How is extrusive igneous rock created
Magma forces out of the ground by pressure, which cools, turning into solid rock
Describe the structure of the earth
- The inner core (hottest, solid, iron and nickel, 55000 degrees)
- The outer core (liquid layer, iron and nickel)
- The mantle (Widest section, 2900km thick, semi-molten rock= magma,
- The crust (outer layer of the earth, 0-60km thick, continental and oceanic)
What is the Asthenosphere
- Solid with the ability to flow (plastic)
- 80km deep
- below the lithosphere
- Made of Rheid
- Plastic properties despite it being solid
What is the mantle divided into
Asthenosphere and Lithosphere
What is the Lithosphere
- Nearer the surface
- Rigid and brittle, is broken into plates
- Cannot flow, is carried by the asthenosphere
Properties of Continental crust
- 30-70km thick
- Very old
- Light (density 2.6)
- lighter coloured rock, eg granite
- made of silica and aluminium
Properties of Oceanic crust
- 6-10km thick
- younger under 200 million years
- Heavier (density 3.0 or more)
- Dark coloured rocks, mainly basalt
- made of silica and magnesium
What is the theory of plate tectonics
- Earth is split into pieces
- Heat rises and falls= convection currents (radioactive decay in core)
- Currents move plates together and apart
- Movement of plates and the activity inside the earth
Theory of Continental Drift
- Alfred Wegener
- Pangea= single continent (300 million years ago)
- Single land mass has split overtime
Evidence of Continental drift
- Continental fit (South American and African continents
- Fossils (Found on matching coastlines of S America and Africa)
- Geological fit- E America and W Africa show ancient rock outcrops continue across both of them (same mineral composition of rocks)
- Tectonic fit- fold mountain fragments were separated across continents (Caledonian mountain belt in Greenland and Canada and England)
- Glaciation (Africa has deposits from glaciers showing it didn’t used to be on the equator)
- Palaeomagnetism
Why continental fit is not perfect
-Sea levels are constantly changing
-Deposition and erosion
=use the continental shelf
what is Palaeomagnetism
Iron rich materials hold a record of the earths magnetic field, when they are formed
Plot the direction of magnetic field of collected rocks
=Apparent polar wondering curve
Rocks in Africa suggest that the pole has curved but actually this leads to the conclusion that the plates have moved.
What is sea floor spreading
- Sonar of the sea floor, shows areas of mountains forming ridges
- Harry Hes theory
- On each side of ridge, the sea floor moves away
- Therefore the ocean becomes wider
- Continuous creation of oceanic crust at MOR
- Convection currents are the driving force
