First a definition: Pre-history is basically the time "before civilization" emerged; in other words, the time before the emergence of cities and the time before the use of writing (the Paleolithic and Neolithic eras).

Humans, and their hominid ancestors, have seemingly inhabited the earth for a very long time now--but still not nearly as long as those dinosaurs--but the period of time studied in this course, that is, the history of world civilizations, occupies only a comparably small fraction of that existence, the last five thousand years.  One of the key precursor conditions to the successful emergence of civilization was the domestication of certain animals and the development of settled, systematic agriculture.  This occurred between 10,000 and 4,000 bce.  Only then could cities, one of the defining features of historical "civilization," develop. 

In recent years, archaeologists and anthropologists have made a number of discoveries at various sites around the world that have pushed back the date of the Agricultural Revolution of the Neolithic period and that have located it in far more places around the world than once thought possible. Scientists, such as Mary Leakey, have also filled in some missing information about the evolution of early humans and hominids (the human-ape family), although much still remains unknown or is just fragmentary. What is now somewhat certain is that the earliest hominid fossils have been dated to four million years ago, while the emergence of Homo sapiens dates to only forty-to-fifty thousand years ago.
If you are interested, check out the Genographic Project, administered by National Geographic, which focuses on ancient human ancestors and migrations.  The project also allows you to check your own ancient ancestors via a DNA test.  (Catherine Damer has shared her experiences with the project; Catherine has also shared some pictures and information on petroglyphs of the Taino that can be seen in Puerto Rico.)
Some recommended online lectures and websites:

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