 Prehistory, human prehistory is the period between the use of the first stone tools see 3.3 million years ago by dominance and the invention of writing systems. The earliest writing systems appeared see 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 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 of their civilizations reached the end of prehistory during the Iron Age. The Free 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 proto-history 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.