Accessibility Even if plenty of water is provided, there may be other limits to its use, such as the time taken for people to travel and queue to collect it. If it takes more than 30 minutes to collect water, the amount they will collect will reduce (see Figure 9.4).
. See also Geologic(al) time scale (below). Geologic(al) time scale: a system of chronologic measurement relating stratigraphy to time that is used by geologists, paleontologists and other earth scientists to describe the timing and relationships between events that have occurred during the history of the Earth.
The Geologic Time Scale. The 4.55 billion-year geologic time scale is subdivided into different time periods of varying lengths. All of Earth history is divided into two great expanses of time. The Precambrian began when Earth first formed 4.55 billion years ago and ended about 570 million years ago.