History of humanity, v. I: Prehistory and the beginnings of civilization

The duration of the period before the invention of writing
This first volume of the new edition of the History of Humanity covers a period extending from the appearance of the first being in the hominid family that can be classified in the genus Homo up to the invention of writing and the advent of the first states, some 5,000 years ago. This ‘prehistoric’ period lasted from 2 to 3 million years. It is so enormously long that few people can imagine it; however, two comparisons may help the reader to visualize this idea.
First, if the 2 1/2 million years or so that have elapsed since the appearance of Homo habilis were represented by a line of a total length of 5 kilometres, each year would count as less than 2 millimetres. The period before writing would represent 4,990 metres, whereas the whole of the so–called ‘historical’ periods (those for which we possess written sources) would be reduced to the last 10 metres. The beginning of the Christian era would be indicated 4 metres from the terminal point and the discovery of America by Columbus only 1 metre from the same terminal point.
Second, the total duration of the existence of humankind might also be compared to a 24–hour day, Homo habilis first appearing when the day was only 1 second old and each century corresponding to 3.456 seconds. The invention of writing and the beginnings of the first states would then be situated less than 3 minutes before midnight and Columbus’s first voyage to America just over 17 seconds before the end of the day.