Outer and inner core

This video explain the discovery of the outer and inner core by Ingrid Lehmann and the reason why the Earth hasn´t cooled off yet.

Plate tectonics. Video

Activity: watch the video and fill in the black of the text below. 

It happens because hot rod _____ heated by the Earth´s _____. Near the surface the rocks spread in two __________ and go sideways, it begins to lose _____. Eventually the much ________ rocks sink. Through the ________ process the Earth´s crust is very slowly dragged apart and is this that ultimately causes the _______ to move. Where the plates __________, the rock on the sea floor containing carbon from the dead plankton is carried deep into the _______. As it descends the little rock is heated so the rock melts releasing __________ ________ and gas is returned back into the atmosphere during an __________. The remarkable cycle is complete.