Composition of the earths structure
The lithosphere consists of continental crust and oceanic crust. Continental crust is 2.7g/cm3 in density, solid, made of granite and has a temperature range between air temperature and 900 degrees Celsius. Oceanic crust is 3.4g/cm3 in density, solid, made of basalt and has a temperature range between air temperature and 900 degrees Celsius. The mantle consists of the asthenosphere and lower mantle. The asthenosphere is 3.4-4.4g/cm3 in density, partially molten, made of perodotite and has a temperature range between 900 and 1600 degrees Celsius. The lower mantle is 4.4-5.6g/cm3 in density, solid, made of perodotite and has a temperature range between 1600 and 4000 degrees Celsius. The core consists of the outer core and inner core. The outer core is 9.9-12.2g/cm3 in density, liquid, made of iron and nickel and has a temperature range between 4000 and 5000 degrees Celsius. The inner core is 15g/cm3 in density, solid, made of iron and nickel and has a temperature range between 5000 and 6000 degrees Celsius.
A GCSE style question and answer
What are the differences between oceanic and continental crust and the rocks that dominate them?
Continental crust is made from granite rocks which has less density minerals where as oceanic crust is made of basal rocks which are more dense. Continental crust is much thicker than oceanic crust, continental crust contains magma which cooled slowly then became larger crystals. Because of the weight and thickness difference between oceanic and continental crust, it balances out the two types of crust.
So, why is the core so hot and how does it drive the process of tectonics?
because of convection currents, plates move
Convection currents are due to heat rising inside the mantle and outer core
Convection currents are driven by the heat of the core, the heat is partly created by the pressure overlying material but also by the radioactivity of the core material itself.
Radioactive decay- some elements are naturally unstable and radioactive. Atoms of these elements release particles from their nuclei and give off heat, this is called radioactive decay
As long as there is a difference in temperature with depth, there will be a cycle of rising and sinking material
Why does the earth act like a magnet?
The earths magnetic field is made by the outer core. As liquid iron in the outer core flows, it produces a magnetic field.
There are many earthquakes in the centre of the Atlantic as that is where a plate margin occurs, there is a constructive plate boundary. It has been explained by ‘hotspot theory’ the idea that there are fixed spots in the mantle where volcanoes rise to the surface ( a bit like a permanent hole in the crust). As the plate shifts off the spot a new volcanic island is created. The Hawaiian islands are in the middle of the pacific ocean yet they are volcanic islands.