Geological changes

Ever since planet Earth was formed there have been changes taking place - to the atmosphere and the rocks. Many of these processes take place so slowly we tend to disregard them, yet important chemical processes are constantly occurring beneath our feet as well as all around us. One example of geological change over a long timescale is the formation of coal. Trees which grew in tropical, swampy conditions did not rot when they died. They were covered first by water, and then by layers of mud. Changes in sea level over the years covered them with more sand and mud, and the weight of these layers squashed the woody material. As these layers were buried deeper and deeper, the heat and pressure gradually converted the material to a mineral - coal.

Rocks - the building blocks of the planet

When we use the word 'rock' we think of a hard, dense lump of material which has come from the ground. In fact there are many different types of rock divided into three main classes - igneous, sedimentary and metamorphic rocks. Rocks consist of crystals or grains of many different minerals, each of which is a chemical compound. The structure and composition of a rock tells us something of its origin, and the processes it has gone through.