Understanding the history of life on Earth requires a grasp of the depth of time and breadth of geographic space. The time involved is vast compared to a human lifetime, and the space in which this history has occurred includes all the water and land surfaces of the world. Establishing the time scales, the timing of events, both relative and absolute, and the patterns of geographic change over time are essential for viewing the motion picture that is the history of life on Earth. The order and timing of events is known as chronology; geographic patterns in the distribution of living things over the Earth is known as biogeography.