Hazards: Plate Tectonics Flashcards
What are the 4 layers of the Earth’s interior?
Inner core
Outer core
Mantle
Crust
What is the Earth’s core made of?
Dense rocks containing iron and nickel alloys
What is the difference between the inner and outer core?
Inner is solid, outer is molten
What is the temperature of the Earth’s core?
5000 C
Which 2 processes heat the Earth’s core?
Primordial heat
Radiogenic heat
Whats primordial heat?
Heat left over from the Earth’s formation
WHat’s radiogenic heat?
Heat produced by the radioactive decay of isotopes
What is the mantle made up of?
Molten and semi-molten rocks containing lighter elements such as silicon and oxygen
What makes the crust so light?
The elements it contains - silicon, oxygen, aluminium, potassium, sodium
What is the lithosphere?
The crust and the rigid upper section of the mantle
How thick is the lithosphere?
80-90km
Which section of the Earth is divided into plates?
The lithosphere
What is the asthenosphere?
The semi-molten layer beneath the lithosphere on which plates float and move
What are the 2 different types of crust?
Oceanic and continental
How thick is continental crust?
30-70km
How thick is oceanic crust?
6-10km
How old is continental crust?
Over 1,500 million years
How old is oceanic crust?
Less than 200 million years
Which is denser, oceanic or continental crust?
Oceanic
What is continental crust composed of?
Granite: SIAL and oxygen
What is oceanic crust composed of?
Basalt: SIMA and oxygen
Who noticed the jigsaw fit in the 17th century?
Francis Bacon
Why did Francis Bacon’s findings not attract any attention?
No one thought continents could move
What is the jigsaw fit?
A description of how continents’ coastlines fit together
Who published the theory of continental drift?
Alfred Wegner
When was the theory of continental drift published?
1912
What supercontinents did Pangea split into?
Laurasia and Gondwanaland
What is the theory of continental drift?
The theory that continents are moving, and splitting from each other to form new continents
What were the 3 pieces of evidence for the theory of continental drift?
Similar fossil remains
Pattern of rocks
Jigsaw fit
Give an example of fossil remains that provide evidence for continental drift.
Mesosaurus remains found in South America and Southern Africa - freshwater and land reptile
What other explanations could there be for the mesosaurus fossils?
Land bridge, ice bridge, separate evolution
Give an example of how rock patterns provide evidence for continental drift.
There is a similar pattern of rock layers on the coasts of Scotland and Canada, suggesting they were once close together or joined
Give evidence for palaeolatitude and palaeoenvironment.
Limestone is formed in shallow, marine environments in the tropics yet is abundant in the UK, suggesting the UK used to be more southernly and tropical
What further evidence developed the theory of plate tectonics?
Sea floor spreading
WHat was the evidence for sea floor spreading?
Identical bands of alternating polarity on either side of the mid-atlantic ridge
Younger rock in the centre
Why are there bands of alternating polarity either side of the mid atlantic ridge?
Iron particles in lava erupted from the ocean floor are aligned with the Earth’s magnetic field. As they solidify they provide a permanent record of the Earth’s polarity at the time of the eruption. The Earth’s polairty reverses at regular intervals forming bands of rock
How often does the Earth’s magnetic field flip?
Every 450,000 years on average
Why does sea floor spreading provide evidence for tectonic plate theory?
Sea floor spreading implies the Earth must be getting bigger but this is not the case, so plates must be being destroyed somewhere else to accomodate the increase in size at ocean ridges
How to tectonic plates move?
Convection currents of magma within the asthenosphere
What is gravitational sliding?
Where the upwelling of magma from ocean ridges forms a higher elevation of the oecan ridge, causing gravity to act down the slope of the ridge
What is slap pull?
The gravity-generated force downwards of oceanic plates as they sink into the mantle
What type of plate boundaries does gravitational sliding occur at?
Constructive
What type of plate boundaries does slab pull occur at?
Destructive
What are the 4 different types of plate boundary?
Constructive
Destructive
Colission
Conservative
What landforms form at constructive plate boundaries?
Ocean ridges, rift valleys and volcanic islands
What landforms form at destructive plate boundaries?
Fold mountains and oceanic trenhces
What are conservative plate boundaries?
Where 2 plates slide past each other parallel to the plate margin
Why is there no volcanic activity at conservative plate margins?
There is no subduction
Example of fold mountains and ocean trench. what are the plates?
Andes
Peru Chile trench
Nazca and South American plates
What are collision boundaries?
Convergent boundary between 2 continental crusts
How are ocean ridges formed?
Oceanic plates move apart
Balsatic lava upwells between plates to form a ridge.
How are rift valleys formed?
Continental plates move apart by convection. Areas of crust drop down between parallel faults to form a valley called a graben. The upstanding blocks on either side are horsts.
Give an example a rift valley? What has formed here?
East African Rift Valley
The volcano Mount Kenya
How do deep sea trenches form?
Where oceanic and continental plates meet, the denser oceanic plate subducts underneath the continental one. The downwarping of the oceanic plate forms a very deep part of the ocean known as a trench.
Why does oceanic crust subduct under continental crust?
Oceanic crust is denser
Why is oceanic crust denser than continental crust?
It contains sima
How to island arcs form?
During subduction the descending plate encounters hotter surroundings and melts. As the material is less dense than the asthenosphere it rises towards the surface as magma plumes. When these reach the surface they form composite volcanoes. If eruptions take place offshore a line of volcanic islands forms.
How do young fold mountains form?
As 2 continental plates converge, little subduction occurs so their edges and sediments between them are forced upwards into fold mountains.
Why is there little subduction between continental plates?
They have much lower density than the underlying layers
