Human prehistory is the period between the use of the first stone tools c. 3.3 million years ago by hominins and the invention of writing systems. The earliest writing systems appeared c. 5,300 years ago, but it took thousands of years for writing to be widely adopted, and it was not used in some human cultures until the 19th century or even until the present. The end of prehistory therefore came at very different dates in different places, and the term is less often used in discussing societies where prehistory ended relatively recently. Sumer in Mesopotamia, the Indus valley civilization, and ancient Egypt were the first civilizations to develop their own scripts and to keep historical records; this took place already during the early Bronze Age. Neighboring civilizations were the first to follow. Most other civilizations reached the end of prehistory during the Iron Age. The three-age system of division of prehistory into the Stone Age, followed by the Bronze Age and Iron Age, remains in use for much of Eurasia and North Africa, but is not generally used in those parts of the world where the working of hard metals arrived abruptly with contact with Eurasian cultures, such as the Americas, Oceania, Australasia and much of Sub-Saharan Africa. These areas also, with some exceptions in Pre-Columbian civilizations in the Americas, did not develop complex writing systems before the arrival of Eurasians, and their prehistory reaches into relatively recent periods; for example 1788 is usually taken as the end of the prehistory of Australia. The period when a culture is written about by others, but has not developed its own writing is often known as the protohistory of the culture. By definition, there are no written records from human prehistory, so dating of prehistoric materials is crucial. Clear techniques for dating were not well-developed until the 19th century. This article is concerned with human prehistory, the time since behaviorally and anatomically modern humans first appeared until the beginning of recorded history. Earlier periods are also called 'prehistoric'; there are separate articles for the overall history of the Earth and the history of life before humans. The notion of 'prehistory' began to surface during the Enlightenment in the work of antiquarians who used the word 'primitive' to describe societies that existed before written records. The first use of the word prehistory in English, however, occurred in the Foreign Quarterly Review in 1836. The use of the geologic time scale for pre-human time periods, and of the three-age system for human prehistory, is a system that emerged during the late nineteenth century in the work of British, German and Scandinavian archeologists, antiquarians and anthropologists. The main source of information for prehistory is archaeology, but some scholars are beginning to make more use of evidence from the natural and social sciences. This view has been articulated by advocates of deep history. The primary researchers into human prehistory are archaeologists and physical anthropologists who use excavation, geologic and geographic surveys, and other scientific analysis to reveal and interpret the nature and behavior of pre-literate and non-literate peoples. Human population geneticists and historical linguists are also providing valuable insight for these questions. Cultural anthropologists help provide context for societal interactions, by which objects of human origin pass among people, allowing an analysis of any article that arises in a human prehistoric context. Therefore, data about prehistory is provided by a wide variety of natural and social sciences, such as paleontology, biology, archaeology, palynology, geology, archaeoastronomy, comparative linguistics, anthropology, molecular genetics and many others.