Tectonic Plates
In GCSE physics curriculum, just below the Earth’s crust the mantle is very solid – further down it is liquid and able to move. CONVECTION CURRENTS in the mantle cause magma (molten rock) to rise to the surface. The force is strong enough to move the solid part of the mantle and the tectonic plates. When the magma reaches the surface, it hardens to form new areas of oceanic crust (SEAFLOOR), pushing the existing floor outwards. This process is called SEAFLOOR SPREADING. It results in seafloor spreading by a few centimetres each year.
New oceanic crust is continuously forming at the crest of an oceanic ridge and old rock is gradually pushed further outwards.
Remeber that in GCSE physics, the Earth has a MAGNETIC FIELD which changes polarity (reverses) every million years or so. Combined with seafloor spreading, this produces stripes of rock alternating polarity. Geologists can work out how quickly new crust is forming from the widths of the stripes. This occurs at CONSTRUCTIVE PLATE BOUNDARIES, where the plates are moving apart.
The Earth’s crust, together with the upper region of the mantle, consists of huge blocks of rock called TECTONIC PLATES in GCSE physcis curriculum.
End of this part. Let's read part III !
Drafted by Gina (Physics)