HAZARDS 2 - Structure of the Earth + Plate Tectonic Theory Flashcards
What is magma?
Molten rock - once it reaches the ground (known as lava)
What is igneous rock?
Rocks formed by the cooling of molten lava, either intrusively or extrusively
What is intrusive magma?
Magma that cools, crystallises and solidifies slowly before reaching the surface
- forms coarse-grained igneous rock e.g. granite
What is extrusive magma?
Lava that is in contact with the air of the sea. It cools, crystallises and solidifies faster than magma underground. Rocks such as Basalt are finer grained with smaller crystals
What is sima?
oceanic crust mainly made up of basalt (silica and magnesium)
What is sial?
Continental crust made of mainly granite rocks (silica and aluminium)
What is the lithosphere?
The crust and upper mantle (tectonic plates found)
What is the asthenosphere?
Weak solid layer below the lithosphere
CRUST
1. What is the thickness of
2. What is it?
2. What are the two types and what are the they made of
- 8-65km
- Solid rock but cracked into tectonic plates
OCEANIC
- sima (lower layer)
- denser > subdued
- younger and thinner
CONTINENTAL
- sial (upper crust layer)
- older + thicker
- less sense
MANTLE
1. Thickness
2. % of the Earth’s volume
3. State
4. State of the upper mantle
- 2,900km
- 84%
- Thick liquid
- Solid
CORE
1. What is it made out of
2. State and why
3. Two elements its made out of
4. What does it create around the Earth
5. Radius and temp
- Compressed due to the interlocking of materials
- Semi-liquid > molecules cannot change state due to pressure
- Iron and nickel
- Magnetic field and radioactive decay (heat source)
- 6000 degrees C and 1220km radius
What is the continental drift theory?
The core is a heat source which generates convection currents in the mantle, which is partly responsible for moving tectonic plates, which move the continents
What does seismic mean?
The types, frequency and size of Earthquakes that happen over a period of time in a certain area
What is Paleomagnetism?
Geophysics concerned with the magnetism in rocks that was induced by the Earth’s magnetic field at the time of their formation
What is polarity?
The relative orientation of the poles > direction of magnetic / electric field
What is subduction?
The side ways or downward movement of the edge of a plate of the Earth’s crust into the mantle beneath another plate
What are convection currents?
A stream of fluid propelled by thermal convection
Who are the 4 key figures that came up with the idea of tectonic movement?
- Ortelius (1596)
- Africa and America torn apart by Earthquakes + flooding - Wegener (1912)
- concept of continental drift > similar fossils on either side of the Atlantic Ocean - Tharp (1953)
- theorised mid ocean ridges were rift valleys by plate motion - Hess (1962)
- concept of sea floor spreading
What is evidence for continental drift?
Sea floor spreading
- evidence of reversed polarity every 400,000 years alongside matching magma types on either side of the eruption zone
Causes of continental drift
- Convention currents
- radioactive decay in the core + heat rising to the surface - Ridge push
- gravity acts on the weight of the crust near the ridge ‘pushes’ the older part of the plate in front - Slab-pull
- the subduction of the crust pulls itself under its own weight into the mantle
