In GCSE Science students will look at the chemical changes which have taken, and do take place on the Earth and in its atmosphere. This is the first of three quizzes on that topic and it looks specifically at the Earth's core and mantle, and at the plates which form the Earth's crust.
The Earth has a layered structure, from the core at its centre, then the mantle above the core, and finally the outer layer, the crust which is divided into several tectonic plates. The crust provides a lot of the raw materials that are used to make things we use and take for granted every day, such as metals, stones and oil. The surface of the Earth is slowly changing but these geological changes are slow, taking tens of thousands of years to become noticeable.
The changes are caused by plate tectonics and weathering. As mentioned before, the Earth's crust is broken into large plates. These plates move around and this movement is thought to be caused by convection currents in the next layer down, the mantle. In some places, like the middle of the Atlantic Ocean, plates move apart and new material erupts from below to fill the gap. In some places they collide head on, creating mountain ranges like the Andes, the Himalayas and the Alps. Here plates are destroyed as they are forced back into the mantle, creating devastating earthquakes and volcanoes. In other places, they slide past each other causing earthquakes but not volcanoes, like the San Andreas fault in the USA.
Moving plates create earthquakes because rocks don't move smoothly past each other. They stick for a while and when enough tension has built up, they suddenly release which is the earthquake. Earthquakes that occur under the sea can cause a tsunami - a fast moving powerful wave of water that can travel a long way inland causing a lot of damage and loss of life. The plates move very slowly, at about the rate your fingernails grow, which is perhaps why scientists took so long to recognise and understand how it all happened.