One of the fundamental principles in the discipline of historical studies, is that for something to be considered part of the historical record, it needs to exist in written form. So, by definition, nothing that happened before the invention of writing can be considered historical. It is literally prehistoric.

Of course, humanity existed on this planet for a long time prior to the invention of writing, and using such disciplines as archaeology, geology and various scientific dating methods (the most well-known of which is radiocarbon dating) we can know much about the activity of human beings and the world in which they lived in prehistoric times.

However, as interesting and important a field of study prehistory is, it actually has little, or even no place, in a historical timeline, if we take into account the strict requirements for something to be considered historical.

The earliest known writing systems were developed by two ancient cultures founded on the banks of the Tigris and Euphrates rivers and the Nile river, namely Sumer and Egypt. With the development of Sumerian Cuneiform and Egyptian Hieroglyph around 5,100 - 5,300 years ago, we therefore have the possibility of historical record keeping for the first time. This is literally (pardon the pun) the beginning of history.

As a result, the World History Timeline begins around the year 3,400 BC/BCE. This, in no way, denies human existence and activity in those periods known as the Stone Age and earlier, but because we have no written records prior to the invention of writing, there are only indirect means available to us for the dating of events. It is therefore not possible for an historical timeline to cover a period much greater that 5,000 years.