Chronology is the science of locating historical events in time. It relies upon chronometry, which is also known as timekeeping, and historiography. Chronology is a part of periodization. It is also a part of the discipline of history including earth history, the earth sciences, and study of the geologic time scale.
The familiar terms calendar and era concern two complementary fundamental concepts of chronology. For example, during eight centuries the calendar belonging to the Christian era, which era was taken in use in the 8th century by Bede, was the Julian calendar, but after the year 1582 it was the Gregorian calendar.
While of critical importance to the historian, methods of determining chronology are used in most disciplines of science, especially astronomy, geology, paleontology and archaeology.
In the absence of written history, with its chronicles and king lists, late 19th century archaeologists found that they could develop relative chronologies based on pottery techniques and styles. In the field of Egyptology, William Flinders Petrie pioneered sequence dating to penetrate pre-dynastic Neolithic times, using groups of contemporary artefacts deposited together at a single time in graves and working backwards methodically from the earliest historical phases of Egypt.