Tectonics- plates and 3 main hazards Flashcards
What are the four distinct layers that make up the earths structure
Inner core, outer core, mantle, crust
What’s the inner core
It’s the centre and is the hottest part of the earth. It’s solid and is made up of iron and nickel with temperatures of up to 5,500 degrees Celsius.
What’s the outer core
It’s the layer surrounding the inner core. It’s liquid and is also made up of iron and nickel. It’s extremely hot, with similar temps to inner core.
What’s the mantle
It’s the widest section of the earth and has a thickness of roughly 2,900km. It’s made up of semi-molten Rock called magma. In the upper parts of it the Rock is hard, but lower down its soft and is beginning to melt.
What’s the crust
It’s the outer layer of the earth, which is thin and is between 0-60km thick. It’s a layer of solid rock upon which we live.
There are two types of crust: continental and oceanic
Differences between continental and oceanic crust
Oceanic is younger and is constantly being created and destroyed. Oceanic is heavier as it has a higher density, so can be subducted and destroyed. Continental is therefore lighter and has less density so it’s permanent and cannot sink, it’s also much older and thicker.
In terms of rock, continental is mostly granite and oceanic is mainly made of basalt.
Why do plates move
Plates at our planets outer surface, move because of the intense heat in the earths core that causes plastic rock in the mantle layer to move. It moves in a pattern called a convection cell that forms when warm material rises, cools and eventually sinks. As cooled material sinks down, it’s warmed and rises again.
So they move due to convection currents and so however the convection currents move is how the plates move. For example if the currents diverge, the plates will move apart.
What’s ridge push
New parts of plate rise because they’re warm and the plate is thin. As hot magma rises to the surface at spreading ridges and forms new crust, the new crust pushes the rest of a plate out of its way.
What’s slab pull
Old parts of a plate are likely to sink down into the mantle at subduction zones because they are colder and thicker than the warm mantle material underneath them.
3 main sources of heat in the earths core
1- heat from when the planet formed which hasn’t been lost yet
2- frictional heating caused by denser core material sinking to the centre of the planet
3- heat from the decay of radioactive elements
Continental drift (wegener’s theory, 1912)
In 1912, Alfred Wegener proposed the theory of continental drift. His idea was that the earths continents were once joined together, but gradually moved apart over millions of years. It offered an explanation of the existence of similar fossils and rocks on continents that are far apart from each other. But it took a long time for this idea to be accepted by other scientists. This theory is now well-established and continental drift is happening as tectonic plates move, with earthquakes and volcanoes often occurring around their edges.
Continental drift (wegener’s theory, 1912)
In 1912, Alfred Wegener proposed the theory of continental drift. His idea was that the earths continents were once joined together, but gradually moved apart over millions of years. It offered an explanation of the existence of similar fossils and rocks on continents that are far apart from each other. But it took a long time for this idea to be accepted by other scientists. This theory is now well-established and continental drift is happening as tectonic plates move, with earthquakes and volcanoes often occurring around their edges.
Sea floor spreading
It’s a process that occurs at the mid-ocean ridges, where oceanic crust is formed through volcanic activity and then gradually moved away from the ridge. Seafood spreading helps explain continental drift. When oceanic plates diverge, tension all stress causes fractures in the lithosphere. Basaltic magma rises up the fractures and cools on the ocean floor to form new sea floor.
In 1940, Harry Hess revealed the shape of the sea floor, using radars and sonars.
What’s the evidence for the sea floor spreading
Continental drift and palaeomagnetism.
Continental drift evidence
- the same types of fossils were found in South America and Africa.
- the shape of the east coast of South America fits the west coast of Africa, like a jigsaw puzzle.
- matching rock formations and mountain chains are found in South America and Africa.
What’s palaeomagnetism
When volcanic lava solidifies or sediments are laid down, magnetic materials (e.g. Iron oxide) align themselves either towards the earths magnetic pole or at an angle dependant on latitude.
How is palaeomagnetism is evidence for how plates move
It shows that the spreading of the sea floor gives magnetic stripes due to cyclical reversal of the earths magnetic field. It also shows that the latitude-dependant dip illustrates that continents used to be situated closer to the equator.
4 main regions of distribution of tectonic activity
- Pacific ring of fire (destructive plate boundary)- subduction, oceanic- e.g. N&S America, Japan, New Zealand
- Eurasian collision zone- continental- e.g. South Europe , turkey, Himalayas
- Constructive (divergent)- continental- e.g. East African rift
- Constructive (divergent)- oceanic- e.g. Mid Atlantic ridge, Iceland
3 volcanic rocks
- Basalt- fine grained, igneous rock, underlying more of the earths surface than any other rock type , associated mainly with constructive plate boundaries.
- Andesite- typically found in lava flows produced by stratovolcanoes, generally formed after an oceanic plate melts during its descent to the subduction zone.
- Rhyolite- formed from granitic magma in continental or continent-margin volcanic eruptions where granitic magma reaches the surface. Rarely produced at oceanic eruptions.
