The theory of plate tectonics tells us that the Earth’s crust is divided into twelve plates (called tectonic plates). These plates act like a kind of skin that covers the planet and moves around extremely slowly (think of inches or centimetres per year), but they are constantly moving and never stop. The movement of these tectonic plates is also the cause of scary earthquakes which happen in many places around the world!
The plates themselves make up the top layer of the Earth that is called the lithosphere; this sits on top of the next layer, called the asthenosphere, which is made up of molten (melted), flowing rock. The centre of the Earth gives of a consistent heat and radiation and this is what causes the rock to become molten. The tectonic plates sit on this layer of flowing rock and are ever-so-slowly moved around the planet by it!
Much like a river or the sea, this molten rock has different types of currents and sometimes the floating plates spread apart to form what’s known as diverging plates. Other times, the current might push them together to form what’s called converging plates. When this happens, one of the plates generally gets pushed under the other and starts to go down into the asthenosphere, where it starts to become molten. A crack or a trench is formed when the plates converge like this, and this has been the cause of many of the deepest parts of the ocean!
Inquiry – Digging Deeper
The theory of plate tectonics is tracked by satellites in space nowadays and this tracking has shown that some of the plates move faster than others. This is what causes the diverging and converging of plates as we mentioned above. This movement also causes continents to shift around the globe. The video above explains this in more detail.