Overview: Geologists, who study the Earth, seek to understand the processes that have shaped our planet throughout its history, creating the world we see around us. To do so, they must reconstruct the Earth's past. Yet how can we tell what happened in distant epochs when there were no witnesses to record events? Around 200 years ago scientists first began to realize that clues to the past lay all around them, in the rocks that make up the Earth's surface. as they learnt how to read these rocks, they began a journey back through time which geologists continue to this day.