Plate tectonics Flashcards
What is the thickness of the crust like?
Varies in thickness:
Under ocean: 5-20km
Under continents: 70km
Describe 4 characteristics of the continental crust.
- 30-70km thick
- over 1500 million years old
- Less dense than the oceanic crust
- Mainly granite rock (sial)
Describe 4 characteristics of the oceanic crust.
- 6-10km
- Less than 200 million years old
- More dense than the continental crust
- Mainly basalt rock (sima)
What is the moho boundary?
The boundary zone between the earth’s crust and the mantle. In this section, there is a change in seismic wave velocity.
Describe the lithosphere.
- the rigid upper section of the crust
- 80-90km thick
- Made from tectonic plates (oceanic and continental)
What is the asthenosphere?
The layer beneath the lithosphere which is semi-molten on which tectonic plates constantly move due to convection currents.
Describe 3 characteristics of the mantle.
- The mantle gets close to melting but does not due to the geothermal gradient.
- Widest section of the earth (2900km thick)
- Semi-molten state due to silicate rock content
How is the upper mantle different to the lower mantle?
In the upper mantle, the rocks are solid whereas in the lower mantle (asthenosphere) there is softer plastic which moves very slowly.
Where is the lithosphere situated?
On top of the asthenosphere.
Describe 3 characteristics of the inner core.
- Solid ball of iron and nickel
- Responsible for the Earth’s internal heat due to energy released by radioactive decay.
- 1,250 km-thick
Describe 3 characteristics of the outer core.
- Semi-molten state
- 2,200 km-thick
Describe 3 characteristics of the asthenosphere.
- Extends from 100 km down to 300 km
- Within the asthenosphere convection currents exist
What is the Earth’s heat engine (the source of the Earth’s internal heat)?
Radiogenic heat is released due to the radioactive decay of isotopes which releases energy in the form of heat. When this migrates to the earth’s surface, convection currents are formed.
