what information did scientists use when developing the geological timeline
To answer these questions, geologists use a special timeline called the Geologic Time Scale. It's a record of the earth's geologic history as scientists have come to understand it by studying the layers in rock.
Scientists use several techniques to determine geological time. Generally, something major happening on earth will be enough reason to determine a new time period in geologic time. For example, a mass extinction of dinosaurs or the end of an ice age are good examples of when a new time period will begin or end.