Prehistory, also known as pre-literary history, is the period of human history between the use of the first stone tools by hominins c. 3.3 million years ago and the beginning of recorded history with the invention of writing systems. The use of symbols, marks, and images appears very early among humans, but the earliest known writing systems appeared c. 5000 years ago. It took thousands of years for writing systems to be widely adopted, with writing spreading to almost all cultures by the 19th century. The end of prehistory therefore came at very different times in different places, and the term is less often used in discussing societies where prehistory ended relatively recently.
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In the early Bronze Age, Sumer in Mesopotamia, the Indus Valley Civilisation, and ancient Egypt were the first civilizations to develop their own scripts and to keep historical records, with their neighbors following. Most other civilizations reached the end of prehistory during the following Iron Age. The three-age division of prehistory into Stone Age, 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 from contact with Eurasian cultures, such as Oceania, Australasia, much of Sub-Saharan Africa, and parts of the Americas. With some exceptions in pre-Columbian civilizations in the Americas, these areas did not develop complex writing systems before the arrival of Eurasians, so 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 system is often known as the protohistory of the culture. By definition, there are no written records from human prehistory, which we can only know from material archaeological and anthropological evidence: prehistoric materials and human remains. These were at first understood by the collection of folklore and by analogy with pre-literate societies observed in modern times. The key step to understanding prehistoric evidence is dating, and reliable dating techniques have developed steadily since the nineteenth century. Further evidence has come from the reconstruction of ancient spoken languages. More recent techniques include forensic chemical analysis to reveal the use and provenance of materials, and genetic analysis of bones to determine kinship and physical characteristics of prehistoric peoples.