The tectonic plates were mapped in the second half of the 20th century
The tectonic plates are a series of plates which cover the entire surface of planet Earth. They can have a depth of up to an estimated 100 km, and are comprised of the entire planets crust, most of the moho, and a tiny piece of the upper mantle. This collective area of rocky planets is generally called the ‘lithosphere’.
The term ‘tectonic plates’ has been historically used by scientists to describe the movement of the lithosphere, however, nowadays the term ‘tectonic plates’ is most widely-used for describing the physical plates themselves, rather than their movement.
The top layer of the tectonic plates – the crust – is continually moving gradually, just like a slow conveyor belt, with new crust appearing on one side of each plate, and disappearing into another boundary it shares with a neighbouring plate.
NOTE* The moho – also know as the ‘Mohorovičić discontinuity’ – is a layer of unknown composition which planet Earth’s crust physically rests upon. It is situated about 5-10 km below the ocean floor and 20-90 km beneath continents. The overall estimated average thickness of the moho is thought to be about 35 km.