The geological timescale and the processes that happen occur over a very long period of time, often millions of years. Each geological period describes a particular, major event that is thought to have happened at that time.
The Earth is thought to be 4,600 million years old. Life is believed to have become dominant on earth 542 million years ago.
The geological periods relate to events which have happened in the Earth's history. For example, during the carboniferous period there were tropical weather conditions in the UK and coal and limestone were formed.
The most recent period in geological time is called the quaternary, when the Ice Age occurred.
Rocks are formed at different times, and are a result of the environment present during that time. For example, chalk is formed in the cretaceous period, as this is when warm tropical seas were present around the shores of the UK.