Structure of the Earth
The Earth is made of a layered structure it has a:
- thin rocky crust
- core (containing iron)
It's difficult to collect information about the structure of the earth. The deepest mines and holes drilled into the crust are only a few Kilometered into the thick crust.
Scientists have to rely on studying the seismic waves (vibrations) caused by earthquakes to understand the structure of the Earth.
Movement of the Lithosphere
The Earth's Lithosphere is the relatively cold, rigid outer part of the Earth, made of the crust and the top part of the mantle.
The top of the lithosphere is 'craked' into several large interlocking pieces called Techtonic Plates:
- OCEANIC PLATES sit under the ocean
- CONTINENTAL PLATES form the continents
The plates sit on top of the mantle because they are LESS DENSE than the mantle. Plates move very slowly (about 2.5cm per year). These movements cause earthquakes and volcanoes at the boundaries between the plates.
What causes Plates to move?
Just below the crust, the mantle is relativey cold and rigid. At greater depths, the mantle becomes a hot and fluid, which means that it can flow. There are convection currents, formed by heat and released from radioactive decay in the core.
Convection currents cause magma (molten rock) to rise to the surface at the boundaries of the plates
When the molten rock solidifies, new igneous rock is formed. This slow movement of the magma causes the plates to move.
Oceanic crust has a higher density than continental crust. When an oceanic plate collides with a continental plate, it dips down and slips under it. This is called subduction. The oceanic plae is partially re-melted as it goes under the continental plate.